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The  Anatomy 

OF  THE 


R.H. WHITEHEAD. 


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ocrATiTrxRrorniVEioLOc 

r  r.i  IT'  c  \  I    (II  ,\'ri  C  IS  \ 


THE 


Anatomy  of  the  Brain 


A  TEXT-BOOK   FOR  MEDICAL 
STUDENTS 


Richard   H.  Whitehead,  IM.E). 

PuOrESSOl!    OF   AXATOIIV    K\   THK    U-VIVKKSIT V   OF  NuRTH    CaROMWA 


Tllttstratea  with  forty-one  engravings 


^%^ 


PHILADELPHIA.      XEW   YOKK.      CHICAGO 

THE  F.  A.  DAYIS  COMPANY,  PUBLISHERS 

1900 


w^ 


COPYRIGHT,  1900, 


THE  F.  A.  DAVIS  COMPANY. 


[Registered  at  Stationers'  Hall,  London,  Eng. 


Philadelphia,  Pa.,  U.  S.  A. : 

The  Medical  Bulletin  Printing-House, 

1916  Cherry  Street. 


PEEFACE. 


Ix  the  preparation  of  tliis  little  book  it  lias  been  the 
author's  aim  to  fnrnish  medical  students  with  a  clear,  accu- 
rate, and  concise  account  of  the  anatomy  of  the  brain,  to  be 
used  as  a  guide  in  their  study  of  that  organ.  Erom  a  work 
of  this  character  it  has  been  thought  best  to  omit  minor  de- 
tails, and  to  exclude,  so  far  as  seemed  possible,  subjects  which 
are  still  matters  of  controversy. 

Kecognizing  the  value  of  a  uniform  nomenclature,  use 
has  been  made  of  the  Latin  terms  adopted  and  recommended 
by  the  German  Anatomical  Society  at  its  meeting  in  Basel, 
to  the  extent  that  they  have  been  inserted,  parenthetically, 
after  the  names  commonly  employed  in  this  country. 

UxivEKSiTY  OF  North  Caeolina, 
April.  1899. 


(iii) 


COE^TEXTS. 

CHAPTEE  I. 
The  Divisions  of  the  Encephalon 1 

CHAPTEE  II. 
The  Sukface  Anatomy  of  the  Encephalon 6 

CHAPTEE  III. 
The  Internal  Anatomy  of  the  Encephalon 34 

CHAPTEE  IV. 

The  Conducting-paths  of  the  Encephalon 86 


(V) 


CHAPTER  I. 
.  The  Divisions  of  the  Encephalox. 

As  THE  division  of  the  encephalon,  or  brain,  into  its 
several  parts  is  based  upon  tbe  embryological  development  of 
that  organ,  it  will  be  necessary  to  briefly  consider  the  early 
development  of  the  central  nervous  system. 


Fig.  1. — Transverse  section  of  first-day  chick  (after  Duval). 
Ep.,  Epiblast.     N.  c,  Neural  canal. 

The  cerebro-spinal  nervous  system  makes  its  first  appear- 
ance as  two  ridges  of  epiblast  bordering  a  groove  in  the 
median  line  (Figs.  1  and  2).  As  these  ridges  increase  in 
elevation,  they  soon  meet  over  the  back  of  the  groove,  which 


Fig.  2. — Transverse  section  of  first-day  chick   (after  Duval). 
Reference  letters  as  in  Fi^.  1. 


thus  becomes  a  canal:  the  neural  canal.  At  this  period  the 
embryonic  nervous  Vystem  may  be  represented  as  a  cylinder 
whose  walls  are  formed  by  epithelial  cells;  in  this  stage  it 
is  called  the  neural  axis.  While  the  great  majority  of  the 
cells  become  differentiated  into  neurones  and  their  supporting 

(1) 


Z  THE    AXATOilT    OF    THE    BEAIN. 

tissue, — the  neuroglia, — some  remain  as  a  lining  to  tlie  canal, 
forming  the  ependymal  epithelium.  The  neural  canal  per- 
sists throughout  life  under  different  names,  and  varies  much 
in  size  in  different  portions  of  the  nervous  system. 

That  part  of  the  neural  axis  which  is  contained  within 
the  embryonic  cranium  and  which  is  to  become  the  brain  is 
seen,  at  a  very  early  stage,  to  be  dilated  into  three  sacs,  or 
vesicles,  known  from  behind  forward  as  the  rhombencephalon, 
mesencephalon,  and  prosencephalon.  A  little  later  the  first 
and  third  of  these  vesicles  are  differentiated  into  two  each, 
the  rhombencephalon  becoming  divided  into  the  myelenceph- 
alon  and  metencephalon,  while  the  prosencephalon  gives  rise 
to  the  diencephalon  and  the  telencephalon.  Thus,  there  are 
now  five  vesicles  from  behind  forward:  the  myelencephalon, 
the  metencephalon,  the  mesencephalon,  the  diencephalon,  and 
the  telencephalon  (Fig.  3). 

From  these  five  vesicles  are  developed  all  the  parts  of 
the  encephalon  which  we  are  about  to  study.  Moreover,  since 
the  five  primary  divisions  maintain  their  individuality  more 
or  less  distinctly  in  the  fully  developed  brain,  those  parts  of 
it  which  a  given  vesicle  produces  are  called  collectively  by 
the  same  name  as  the  parent-vesicle.  In  other  words,  the 
vesicle  bears  the  same  name  both  in  the  undeveloped  and  in 
the  mature  state. 

The  encephalon  is  divided  into  five  parts,  then,  as  fol- 
lows (Figs.  3,  4,  and  5): — 

1.  The  myelencephalon,  or  the  medulla  oblongata. 

2.  The  metencephalon,  composed  of  the  pons  Varolii 
and  the  cerebellum.  The  pons  Varolii  is  developed  from  that 
portion  of  the  metencephalon  which  lies  ventral  to  the  neural 
canal,  the  part  which  lies  dorsal  to  the  canal  producing  the 
cerebellum.  The  most  anterior  portion  of  the  metencephalon 
may  be  individualized  into  a  separate  division  under  the  name 
of  the  isthmus  of  the  rhombencephalon.  The  neural  canal 
in  the  region  of  the  rhombencephalon  becomes  the  fourth 
ventricle. 

3.  The  mesencephalon,  consisting  of  the  corpora  quad- 
rigemina  dorsal  to,  and  the  peduncles  of  the  cerebrum  ven- 


THE    DIVISION'S    OF    THE    ENCEPHALON-. 


Fig.  3. — Sagittal  section  of  brain  of  one-month  human  embryo  (after 
His).  /.  Myelencephalon :  /.I,  Ventral  portion;  1.2,  dorsal  portion. 
//.  Meteneephalon:  7/.1,  Pons  Varolii;  II. 2,  cerebellum.  ///.  Isthmus 
rhombencephali :  777.1,  Ventral  portion;  777.2,  dorsal  portion.  lY.  Mesen- 
cephalon: 7y.l,  Pedunculi  cerebri;  77.2,  corpora  quadrigemina.  Y.  Dien- 
cephalon:  F.l,  Pars  mamillaris  hypothalami;  Y.2,  thalamus;  F.3,  meta- 
thalamus;  7.4,  epithalamus.  77.  Telencephalon:  77.1,  Pars  optica  hypo- 
thalami;   77.2,  corpus  striatum;    77.3,  rhinencephalon;    77.4,  pallium. 


4  THE   ANATOMY    OF    THE    BRAIN. 

tral  to,  the  neural  canal,  which  here  is  called  the  aqueduct  of 
Sylvius. 

4.  The  diencephalon.  This  is  divided  into  the  thala- 
niencephalon  dorsal  to,  and  the  hypothalamus  ventral  to,  the 
neural  canal.  The  thalamencephalon  is  subdivided  on  each 
side  of  the  median  line  into  the  thalamus,  the  epithalamus 
(or  the  pineal  body  and  habenula),  and  the  metathalamus  (or 
the  geniculate  bodies).  The  neural  canal  in  this  situation  is 
called  the  third  ventricle.  Ventral  to  it  is  the  hypothalamus, 
only  the  posterior  part  of  which,  however,  belongs  to  the 
•diencephalon. 

5.  The  telencephalon.  This  consists  of  the  hemispheres 
dorsal  to  the  neural  canal,  while  a  small  ventral  portion  forms 
the  anterior  part  of  the  hypothalamus.  Here  the  neural  canal 
develops  into  the  lateral  ventricles.  As  the  result  of  very  rapid 
growth,  especially  in  its  lateral  portions,  the  telencephalon 
soon  outgrows  its  neighbors,  and  overlaps  the  diencephalon 
and  mesencephalon.  To  these  three  divisions — telencepha- 
lon, diencephalon,  and  mesencephalon — collectively  the  term 
cerebrum  is  commonly  applied. 


THE    DIVISIOXS    OF    THE    EXCEPHALOX. 


Fig.  4. — Sagittal  section  of  brain  of  mammal    (after  Edinger). 
Keference  numbers  as  in  Fig.  3. 


Fig.  5. — Sagittal  section  of  human  brain   (after  His). 
Eeference  numbers  as  in  Fig.  3. 


CHAPTER  II. 

The  Surface  A^'ATOMY  of  tiie  Excephalox. 

THE    SURFACE    AXATOMY    OF    THE    MYELEXCEPHALOX. 

The  myelenceplialon  or  tlie  medulla  oblongata  extends 
between  the  spinal  cord  behind  and  the  pons  Varolii  in  front. 
It  is  somewhat  conical  in  shape,  with  its  base  forward  and 
on  a  plane  dorsal  to  the  smaller  extremity,  which  is  contin- 
uous with  the  spinal  cord.  It  is  about  one  and  one-quarter 
inches  long,  and  its  widest  diameter  measures  nearly  one  inch. 
It  rests  upon  the  posterior  part  of  the  concave  surface  of  the 
basilar  process  of  the  occiput.  For  purposes  of  description  it 
may  be  divided  into  a  ventral  surface,  a  dorsal  surface,  and 
two  lateral  surfaces. 

The  ventral  surface  (Eig.  6)  presents  in  the  median  line 
a  well-marked  longitudinal  groove, — the  ventral  median  fis- 
sure (fissura  mediana  anterior), — on  each  side  of  which  is  a 
rounded  band,  the  pyramid  fpyramis).  Xear  the  spinal  cord 
the  fissure  is  almost  obliterated  by  fibres  which  pass'  across  from 
one  p;sTamid  into  the  other;  this  is  called  the  decussation  of 
the  pyramids  (decussatio  pyramidum).  Lateral  to  each  pyra- 
mid and  separating  the  ventral  from  the  lateral  surface  is  the 
ventro-lateral  sulcus  (sulcus  lateralis  anterior),  from  which 
emerge  the  root-fibres  of  the  twelfth  cranial,  or'  hypoglossal, 
nerve   (nervus  hypoglossus). 

The  lateral  surface  (Eig.  6)  in  its  posterior  half  is  known 
as  the  lateral  tract  (funiculus  lateralis).  Its  anterior  half  is 
occupied  by  an  oval  mass  called  the  olive  (oliva).  Each 
lateral  is  separated  from  the  dorsal  surface  of  the  medulla 
by  the  dorso-lateral  sulcus  (sulcus  lateralis  posterior),  from 
which  many  nerve-fibres  escape  to  soon  unite  and' form  three 
nerves;  from  before  backward  these  are  the  ninth  (nervus 
glosso-pharyngeus),  the  tenth  (nervus  vagus),  and  the  acces- 
sory portion  of  the  eleventh  (nervus  accessorius)  cranial  nerves. 
It  will  be  noticed  that  the  posterior  part  of  this  sulcus  is  in- 

(6) 


THE    SUEFACE    ANATOIIT    OF    THE    EXCEPHALOX. 


Op,n 


C.fnam.^ 


^^J't^^Opck 


Sabs  int 
Dp-tr 

.-nc. 


Fig.  6. — Roman  numerals  refer  to  cranial  nerves.  C'.l,  First  cervical 
spinal  nerve.  C.  mam.,  Corpus  mamillare.  Op.  n.,  Optic  nerve.  Inf.,  In- 
fundibulum.  Op.  ch.,  Optic  chiasm.  Siibs.  int.,  Substantia  interpeduncu- 
laris.  Op.  tr.,  Optic  tract.  P.  C,  Peduncle  of  cerebrum.  G.  g.  I.,  Lateral 
geniculate  body.  Sul.  6.,  Basilar  sulcus.  M.  p.  c,  Middle  peduncle  of  cere- 
bellum. F.,  Flocculus.  F.  h.,  Horizontal  fissure.  0.,  Olive.  T.  I.  s.,  Ventro- 
lateral sulcus.  Pijr.,  Pyramid.  T.  m.  f..  Ventral  median  fissure.  (After 
Van   Gehuchten. ) 


»  THE   ANATOMY    OF   THE    BEAIN. 

terrupted'by  the  passing  of  a  part  of  the  lateral  tract  to  the 
dorsal  surface  of  the  medulla. 

The  ventral  and  lateral  surfaces  of  the  medulla  are  clearly 
limited  from  the  pons  Varolii  by  a  transverse  groove.  In  this 
groove  appear  the  root-fibres  of  three  cranial  nerves:  the 
sixth  (nervus  abducens),  opposite  the  pyramid;  the  seventh 
(nervus  facialis),  opposite  the  dorso-lateral  sulcus;  and  the 
eighth  (nervus  acusticus),  still  farther  lateral. 

The  dorsal  surface  (Fig.  7)  may  be  divided  into  an  ante- 
rior and  a  posterior  half.  The  latter  resembles  the  spinal 
cord;  here  we  find  in  the  median  line  the  dorsal  median 
fissure  (fissura  mediana  posterior),  and  on  each  side  of  it  the 
continuation  of  the  dorsal  funiculi  of  the  cord, — the  funiculus 
of  Goll  (funiculus  gracilis),  next  to  the  median  fissure  and 
separated  laterally  from  the  funiculus  of  Burdach  (funiculus 
cuneatus)  by  the  paramedian  fissure.  These  two  funiculi 
terminate  forward,  the  former  in  a  small  elevation  called  the 
clava,  the  latter  in  a  less  distinct  elevation  extending  farther 
forward  called  the  cuneate  tubercle. 

Owing  to  the  termination  of  these  dorsal  funiculi  and 
to  an  increase  in  the  transverse  diameter  of  the  neural  canal 
at  this  point,  the  anterior  division  of  the  dorsal  surface  pre- 
sents a  depression,  which  is  bounded  laterally  by  a  white  cord : 
the  corpus  restiforme.  The  two  corpora  restiformia  diverge 
to  enter  the  cerebellum,  leaving  thus  between  them  a  tri- 
angular depression,  which  is  the  floor  of  the  neural  canal, 
and  is  called  the  calamus  scriptorius.  As  it  is  also  the  poste- 
rior (inferior)  part  of  the  floor  (fossa  rhomboidea)  of  the 
fou.rth  ventricle,  which  is  the  neural  canal  of  the  rhomben- 
cephalon, it  is  called  the  pars  inferior  fossse  rhomboidese. 
The  base  of  the  triangular  depression  is  forward,  and  nearly 
corresponds  to  some  fibres  seen  crossing  the  fioor  of  the  ven- 
tricle on  each  side:  the  striae  acusticse  (striae  inedullares). 
These  emerge  from  the  longitudinal  median  sulcus,  which  is 
continuous,  not  with  the  dorsal  median  fissure  of  the  medulla, 
but  with  the  floor  of  the  central  canal  continued  from  the 
cord  into  the  medulla.  Between  this  sulcus  and  the  corpus 
restiforme  the  dorsal  surface  on  each  side  may  be  divided 
into  three  triangles,  as  follows:    Bordering  the  sulcus- is  a 


THE    SUKFACE    AXATOMY    OF   THE   EXCEPHALON^. 


Nuc.  Cmid, 

Sui 

\ 

.     Nuc.caud. 

ThaL^    _.-^' 

1 

-  -K 

P-hn...; 

^^ -I  "     - 

S'T 

'  F^ 

'-'"'' \i 

'    -  Lat.lem. 
.  A.p.c. 

^^    .3ta. 

-:-:-- M.p.c. 
C.r. 

Al.cin.-  - 

#.,_ 

-'■C.tuh. 

CL  -  - 

\a:\  . 

F.B. 

! 
i 

_  _!-- 

-F.G. 

Dlsuh 

i 

-   --- 

D.m.j^. 

L.tr,- 

-- 

'- 

P.sul 

Fig.  7. — Sul.  ch.,  Choiioid  sulcus.  Nuc.  caud.,  Nucleus  caudatus.  Thai., 
Thalamus.  St.  m.,  Stria  medullaris.  P.  b.,  Pineal  body.  G.  q.,  Corpora 
quadrigemina.  P^ilv.,  Pulvinar.  Fr.,  Frenulum.  Lat.  lem.,  Medial  lemniscus. 
A.  p.  c,  Anterior  peduncle  of  cerebellum.  M.  p.  c,  Middle  peduncle  of  cere- 
bellum. St.  a.,  Acoustic  striae.  C.  r.,  Corpus  restiforme.  G.  tub.,  Cuneate 
tubercle.  F.  O.,  Funiculus  of  Goll.  D.  m.  f.,  Dorsal  median  fissure.  P.  sul, 
Paramedian  sulcus.  L.  tr.,  Lateral  tract.  D.  I.  sul.,  Dorso-lateral  sulcus. 
F.  B.,  Funiculus  of  Burdach.  CI.,  Clava.  Al.  cin.,  Ala  cinerea.  T.  h.,  Hypo- 
glossal triangle.  A.  a.,  Acoustic  area.  G.  f.,  Colliculus  facialis.  S.  Urn., 
Sulcus  limitans.  E.  m.,  Eminentia  medialis.  Y.  Y.,  Anterior  medullary 
velum.  IT,  Trochlear  nerve.  G.  g.  m.,  Medial  geniculate  body.  G.  g.  I., 
Lateral  geniculate  body.  P.  Ir.,  Posterior  brachium  of  mesencephalon. 
(After   Van   Gehuchten.) 


10  THE   AXATOMT    OF    THE    BEAIX. 

small  triangular  area  ^vitll  its  base  forward;  this  is  the  land- 
mark of  the  nucleus  of  the  twelfth  cranial  or  hypoglossal 
nerye,  and  is  called,  therefore,  the  hypoglossal  triangle  (tri- 
gonnm  neryi  hypoglossi).  The  hypoglossal  triangle  is  bounded 
laterally  by  a  faint  sulcus,  the  sulcus  limitans,  which  sep- 
arates it  from  the  second  triangular  area,  which  is  somewhat 
darker  in  color,  and  is  known  as  the  ala  cinerea;  this  has  its 
apex  forward,  and  is  the  landmark  of  the  sensory  nuclei  of 
the  ninth  and  tenth  cranial  nerves.  The  third  triangle  is 
found  between  the  ala  cinerea  and  the  corpus  restiforme;  it 
has  its  base  forward  at  the  striae  acusticse,  and  is  the  posterior 
portion  of  the  acoustic  area  (area  acustica),  containing  nuclei 
of  the  eighth  cranial,  or  acoustic,  nerve. 

THE    SURFACE    A^'ATOMY    OF    THE    METEXCEPHALOX, 

The  metencephalon  is  composed  of  the  pons  Varolii  and 
the  cerebellum. 

The  Poxs  Varolii. — This  presents  for  study  two  sur- 
faces:   a  ventral  and  a  dorsal. 

The  ventral  surface  (Tig.  6)  is  situated  between  the  cere- 
bral peduncles  in  front,  the  medulla  oblongata  behind,  and 
the  cerebellum  laterally.  It  is  constituted  by  a  broad  layer 
of  transverse  fibres,  which  contracts  on  each  side,  and  enters 
the  cerebellum  as  its.  middle  peduncle  (brachium  pontis).  In 
the  median  line  is  an  antero-posterior  groove, — the  •  basilar 
sulcus  (sulcus  basilaris)  for  the  basilar  artery, — and  on  each 
side  of  this  a  ridge  thrown  up  by  the  passage  of  the  fibres 
which  constitute  the  pyramid  in  the  medulla.  Laterally  ap-, 
pear  the  root-fibres  of  the  fifth  cranial,  or  trigeminal,  nerve 
(nervus  trigeminus),  piercing  this  surface  of  the  pons. 

To  examine  the  dorsal  surface  it  is  necessary  to  remove 
the  cerebellum.  It  is  then  seen  that  this  surface  consists  of 
an  elevated  cord  on  each  side,  with  a  depression  between  (Fig. 
7).  The  cords  are  the  anterior  peduncles  of  the  cerebellum 
(brachia  conjunctiva),  which  converge  toward  the  mesenceph- 
alon, where  they  disappear.  Lateral  to  the  peduncle  a  band 
of  fibres  can  be  seen  winding  forward  and  dorsalward  to  reach 
the  mesencephalon;    this  is  the  lateral  lemniscus  (lemniscus 


TI[E    SUEFACE    AXATOMY    OF    THE    EXCEPnALOX. 


11 


Cor/j.cal. 


Post  com. 


h  pi 

^Antcom.       ^' 
_'■--- -Op.r: 
~       -IvF.r- 

■^  Mas.  int. 
-  Of-ch. 

Tul.cin 


-r-M 


Fig.  S.Spl.,  Splenium.  Thai.,  Thalamus.  St.  med.,  Medullary  stria. ^ 
Sul.  hyp.,  Sulcus  hypothalamicus.  Corp.  cal.,  Corpus  eallosum.  Sep.  pel.. 
Septum  pellucidum.  G.,  Genu  of  corpus  eallosum.  Col.  for.,  Column  of 
fornix.  C7i.  pi.,  Chorioid  plexus  of  lateral  ventricle.  L.  t.,  Lamina  terminalis. 
Ant.  com.,  Anterior  commissure.  Op.  r.,  Optic  recess.  Inf.  r.,  Recess  of 
infundibulum.  Mas.  int.,  Massa  intermedia.  Op.  cli..  Optic  chiasm.  Tut),  cin.. 
Tuber  cinereum.  Eyp.,  Hypophysis.  Ill,  Oculomotor  nerve.  C.  mam..  Cor- 
pus mamillare.  P.  C,  Peduncle  of  cerebrum.  P.,  Pons  Varolii.  Aq.  S., 
Aqueduct  of  Sylvius.  Y.  V.,  Anterior  medullary  velum.  J/..  ]\Iedulla  ob- 
longata. F.  v.,  Fourth  ventricle.  P.  v.  p.,  Posterior  vermiform  process.  C, 
Cerebellum.  A.  v.  p..  Anterior  vermiform  process.  Post,  com.,  Posterior  com- 
missure. P.  b.,  Pineal  body.  C.  q.,  Corpora  quadrigemina.  (After  Van 
Gehuchten.) 


12  THE   AXATOMY    OF    THE    BEAIK". 

lateralis).  The  depression  between  the  pednncles  is  triangnlar 
in  shape,  and  forms  the  anterior  part  of  the  floor  of  the  fourth 
ventricle.  It  is  covered  over  by  a  thin,  white  lamina,  stretch- 
ing across  from  one  peduncle  to  the  other,  continuous  in  front 
with  the  mesencephalon,  behind  with  the  cerebellum;  it  is 
known  as  the  valve  of  Yieussens,  or  anterior  medullary  velum 
(velum  medullare  anterius),  and  through  it  the  fourth  cranial 
nerve  (nervus  trochlearis)  escapes  on  each  side.  ,  The  depres; 
sion  has  its  base  backward,  coinciding  with  that  of  the  calamus 
scriptorius  of  the  medulla,  between  which  and  the  pons  there 
is  no  distinct  boundary  on  the  dorsal  aspect.  In  the  median 
line  is  seen  the  forward  continuation  of  the  dorsal  median 
sulcus  of  the  medulla,  and  laterally  the  forward  prolongation 
of  the  sulcus  limitans.  These  two  sulci  inclose  between  them 
a  ridge,  the  medial  eminence  (eminentia  medialis),  which  is 
the  landmark  of  the  nucleus  of  the  sixth  cranial  nerve.  On 
each  side  of  the  median  sulcus  at  about  its  middle  the  floor 
of  the  ventricle  is  thrown  up  into  a  small  rounded  eminence 
by  the  root-fibres  of  the  seventh  cranial  nerve,  called  the  col- 
liculus  facialis.  In  front  the  sulcus  limitans  deepens  some- 
what to  form  the  anterior  fovea  (fovea  superior);  behind,  on 
the  medulla,  at  the  apex  of  the  ala  cinerea,  it,  in  like  manner, 
forms  the  posterior  fovea  (fovea  inferior).  Lateral  to  the 
anterior  fovea,  at  the  line  of  junction  of  the  floor  with  the 
side  of  the  ventricle,  is  a  bluish  spot,  the  locus  coeruleus,  which 
is  the  landmark  of  the  nucleus  of  the  trigeminal  nerve.  In 
the  angle  formed  by  the  corpus  restiforme  behind  and  the 
anterior  peduncle  in  front,  lateral  to  the  sulcus  limitans,  is 
the  acoustic  area  (area  aeustica),  which  is  situated  partly  on 
the  pons  and  partly  on  the  medulla,  and  is  bisected  by  striae 
acusticse. 

The  Ceeebellu:\[. — On  external  examination  the  cere- 
bellum appears  laminated,  consisting  of  plates  of  nervous 
matter  separated  by  narrow  sulci.  In  shape  it  is  rather  oblong, 
and  is  about  four  inches  wide  and  two  inches  in  its  dorso- 
ventral  diameter.  It  occupies  the  inferior  occipital  fossae  of 
the  skull.  It  may  be  divided  into  an  anterior,  a  posterior,  and 
a  ventral  surface.  The  anterior  surface  (Fig.  8)  is  marked 
in  the  median  line  by  an  elevated  portion  called  the  anterior 


THE    SURFACE    ANATOMY    OF    THE    ENCEPHALON. 


13 


Mpc 
'  Sulh. 


/     Tloc. 


Fig.  9. — y.  «.,  Ventral  extremity  of  anterior  vermiform  process.  F.  F., 
Anterior  medullary  velum.  A.  p.  c,  Anterior  peduncle  of  cerebellum. 
Md.  av.,  Nidus  avis.  M.  j).  c,  Middle  peduncle  of  cerebellum.  Svl.  h.,  Hori- 
zontal sulcus.  Floe,  Flocculus.  C.  v.,  Corpus  restiforme.  P.  m.  v.,  Posterior 
medullary  velum.-    Nod.,  Nodulus.     (After  Van  Gehuchten.) 


14  THE   ANATOMY    OF    THE    BKAIN. 

(snperior)  vermiform  process  (vermis  superior),  terminating 
ventrally  at  a  notch, — the  ventral  incisure  (incisura  ante- 
rior),— and  dorsally  at  a  deeper  notch, — the  dorsal  incisure 
(incisura  posterior).  On  the  posterior  surface  opposite  to  the 
anterior  vermiform  process  is  a  deep  groove,  the  vallecula,  in 
the  bottom  of  which  is  the  posterior  (inferior)  vermiform 
process  (vermis  inferior).  It  will  be  noticed  that  the  two 
vermiform  processes  are  continuous  dorsally  and  form  one 
lobe,  which  is  termed  the  worm  (vermis).  The  worm  and  the 
notches  form  the  landmarks  for  dividing  the  remainder  of  the 
cerebellum  into  two  hemispheres.  The  cerebellum  has  been 
further  subdivided  into  numerous  lobes,  but,  as  our  knowledge 
of  the  functions  of  the  cerebellum  is  so  imperfect,  their 
names,  which  are  in  many  instances  fanciful,  may  be  here 
omitted. 

To  examine  the  ventral  surface,  the  cerebellum  must  be 
removed  from  its  connections  by  severing  its  various  peduncles. 
When  this  has  been  done  (Fig.  9)  we  find  in  the  median  line 
the  ventral  extremity  of  the  anterior  vermiform  process  in 
front,  and  the  ventral  extremity  of  the  posterior  vermiform 
process,  called  the  nodulus,  behind.  The  former  rests  upon  a 
thin  sheet  of  white  matter,  which  will  be  recognized  as  the  ante- 
rior medullary  velum,  over  which  the  worm  sends  forward  a 
thiPi 'Strip :  the  lingula.  On  each  side  the  velum  is  attached  to 
the  anterior  peduncle,  the  cross  sections  of  which  are  here  seen. 
Posterior  to  the  anterior  medullary  velum  is  the  transverse 
fissure  (fissura  transversa),  leading  into  a  cleft,  or  cul-de-sac, 
called  the  tent,  or  "bird's  nest"  (nidus  avis).  Lateral  to  this  is 
the  section  of  the  corpus  restiforme,  and  lateral  to  it  the  larger 
section  of  the  middle  peduncle.  Still  farther  lateral  is  the 
beginning  of  a  fissure  which  can  be  traced  around  the  circum- 
ference of  the  cerebellum  to  a  corresponding  point  on  the  op- 
posite side:  the  horizontal  fissure  (fissura  horizontalis).  In  the 
commencement  of  this  fissure  is  a  quite  distinct  lobule:  the 
flocculus.  From  the  flocculus  a  delicate  layer  of  white  matter 
runs  toward  the  median  line,  and  crosses  on  the  anterior  aspect 
of  the  nodulus  to  gain  the  flocculus  of  the  opposite  side ;  this 
is  the  posterior  medullary  velum  (velum  medullare  posterius). 
It  is  thus  seen  that  the  tent  is  a  cleft  in  the  white  matter  of 


THE    SUEFACE   ANATOMY    OF    THE    ENCEPHALOX.  15 

the  cerebellum  between  tbe  two  medullary  vela.  It  is  pro- 
longed on  eacb  side  as  far  as  tbe  middle  peduncle,  wbicb  lateral 
prolongations,  as  we  shall  hereafter  see,  are  the  lateral  recesses 
of  the  fourth  ventricle,  toward  which  cavity  this  surface  of  the 
cerebellum  looks. 

THE    ISTHMUS    OF    THE    KHOMBEIS^CEPHALO^^. 

The  isthmus  of  the  rhombencephalon  (isthmus  rhomben- 
cephali)  is  the  name  given  to  the  most  anterior  part  of  the 
rhombencephalon,  uniting  that  vesicle  to  the  mesencephalon. 
In  the  embryo  it  exists  as  a  separate  vesicle,  but  in  the  de- 
veloped brain  it  has  no  distinct  boundaries.  Its  dorsal  portion 
consists  of  the  anterior  peduncles  of  the  cerebellum  and  the 
anterior  medullary  velum;  these  we  have  described  as  a  part 
of  the  pons  Varolii.  Its  ventral  portion  is  furnished  by  the 
beginning  of  the  cerebral  peduncles,  including  the  nuclei  of 
the  fourth  pair  of  cranial  nerves ;  these  we  shall  study  in  con- 
nection with  the  mesencephalon. 

THE    FOUKTH    VENTKICLE. 

The  fourth  ventricle  (ventriculus  quartus)  is  the  neural 
canal  in  the  rhombencephalon  (Fig.  7).  It  may  be  considered 
as  having  a  floor,  a  roof,  and  two  sides.  The  floor  (fossa  rhom- 
boidea)  is  diamond-shaped,  and  is  furnished  by  the  triangular 
depression  on  the  dorsal  surface  of  the  pons  in  front,  and  by 
the  calamus  scriptorius  of  the  medulla  behind.  If  we  regard 
the  isthmus  of  the  rhombencephalon  as  a  separate  division, 
there  are  three  contributors  to  the  floor:  the  isthmus  furnish- 
ing the  anterior  portion  (pars  superior) ;  the  pons  forming  the 
middle  portion  (pars  intermedia), — the  part  included  between 
lines  embracing  the  middle  peduncles  of  the  cerebellum; 
while  the  medulla  contributes  the  posterior  portion  (pars  in- 
ferior fossae  rhomboidese).  The  appearances  in  the  floor  of 
the  ventricle  have  been  already  described  in  the  accounts  of 
the  medulla  and  of  the  pons. 

The  sides  or  lateral  boundaries  of  this  diamond-shaped 
space  are  furnished  in  front  by  the  anterior  peduncles  of  the 
cerebellum  and  behind  by  the  corpora  restiformia. 


16  THE   AX  ATOMY    OF    THE    BEAIiST. 

The  roof  of  the  ventricle  in  its  anterior  portion  is  the 
anterior  medullary  velnm;  the  posterior  part  of  the  roof 
is  furnished  by  a  reflection  of  the  pia  mater  known  as  the 
tela  chorioidea.  To  gain  a  correct  conception  of  this,  part 
of  the  roof  it  will  be  necessary  to  revert,  for  a  moment, 
to  the  development  of  the  rhombencephalon.  The  epithe- 
lial cells  forming  the  dorsal  wall  of  the  embryonic  rhomb- 
encephalon produce  the  anterior  medullary  velum  in  front, 
and  the  worm  and  posterior  medullary,  velum  of  the  cere- 
bellum in  the  middle;  but,  along  a  line  corresponding  to  the 
free  edge  of  the  posterior  medullary  velum,  this  epithelium 
ceases  to  develop  nervous  tissue.  In  the  mature  brain,  there- 
fore, the  dorsal  wall  of  the  rhombencephalon  reaches,  in  its 
primitive  condition  as  a  layer  of  epithelial  cells,  from  the  edge 
of  the  posterior  medullary  velum  in  front  to  the  medulla  be- 
hind (Fig.  4).  This  layer  is  consequently  triangular,  with  its 
base  at  the  edge  of  the  velum,  its  apex  continuous  with  the 
epithelium  lining  the  dorsal  wall  of  the  central  canal  of  the 
medulla,  and  its  sides  attached  to  the  medial  surfaces  of  the 
corpora  restif  ormia,  where  the  production  of  nervous  substance 
is  resumed.  'Now,  the  pia  mater,  adhering  closely  to  the  en- 
cephalon  at  all  points,  enters  the  space  between  the  cerebellum 
and  the  medulla,  and  invaginates  this  epithelial  membrane, 
p  ashing  it  ahead  as  far  as  the  lateral  recesses.  This  fold  of  pia 
mater  is  the  tela  chorioidea.  The  epithelium  adheres  to  its 
ventricular  aspect,  and  is  therefore  called  the  lamina  chorioidea 
epithelialis.  As  a  matter  of  fact,  the  epithelium  is  the  j:rue 
roof  of  the  ventricle ;  but,  since  it  is  adherent  to  the  tela,  and 
is  torn  from  its  other  attachments  when  the  tela  is  removed, 
the  latter  is  commonly  called  the  roof.  On  its  ventricular  sur- 
face the  tela  presents  a  row  of  vascular  tufts  on  each  side  of 
the  median  line:  the  median  chorioid  plexus  (plexus  chori- 
oideus  ventriculi  quarti).  N'ear  its  anterior  margin  the  plexuses 
turn  and  run  lateralward,  and  in  this  situation  are  called  the 
lateral  chorioid  plexuses.  There  is  frequently  an  opening  in 
the  tela  known  as  the  foramen  of  Magendie ;  so  that  the  cavity 
of  the  fourth  ventricle  communicates  with  the  space  between 
the  pia  mater  and  the  arachnoid. 

The  ventricle  has  four  angles :  an  anterior,  where  it  is  con- 


THE    SUEFACE   ANATOMY    OF    THE    ENCEPHALON. 


17 


Col.Pon 
Mtha} 


Mas.ink 


c 

H.nuc.caad. 
.,.  Col. fori 

m. 

J.t.thal 

^JVuc.caud 

VenM 
..-  Tn^,hah. 
.  Thai, 
Sul.ch. 
J^nuc.caue/. 

Pulv 


Fig.  10. — A.  c,  Anterior  horn  of  lateral  ventricle.  H.  ntic.  caud.,  Head 
of  caudate  nucleus.  Col.  for.,  Column  of  fornix.  F.  M.,  Foramen  of  Monro. 
A.  t.  thai.,  Anterior  tubercle  of  thalamus.  St.  term..  Stria  terminalis.  Nuc. 
caud.,  Nucleus  caudatus.  Yen.  Ill,  Third  ventricle.  Trig.  Ml).,  Trigonum 
habenulae.  Thai.,  Thalamus.  Siil.  ch.,  Chorioidal  sulcus.  T.  nuc.  caud., 
Tail  of  nucleus  caudatus.  Pulv.,  Pulvinar.  Teg.,  Tegmentum.  T.  T.,  An- 
terior medullary  velum.  G.  q.,  Corpora  quadrigemina.  Hab.,  Habenula. 
P.  h..  Pineal  body.  Med.  St.,  Medullary  stria.  Has.  int.,  Massa  intermedia. 
Sep.  pel..  Septum  pellucidum.  A.  p.  c,  Anterior  peduncle  of  cerebellum. 
(After  Van  Gehuchten.) 


18  THE   ANATOMY    OF    THE   BEAIN. 

tinuoiis  .with,  tile  aqueduct  of  Sylvius ;  a  posterior,  where  it  is 
continuous  with  the  canal  of  the  medulla  between  the  two 
clavse;  and  two  lateral.  The  latter  are  the  angular  intervals 
between  the  diverging  corpora  restiformia  and  the  anterior 
jjeduncles  of  the  cerebellum.  As  we  have  seen,  these  are  the 
lateral  prolongations  of  the  tent  of  the  cerebellum,  and  each 
is  here  called  a  lateral  recess  (recessus  lateralis)  of  the  ventricle. 

THE    SURFACE    ANATOMY    OF    THE    MESENCEPHALON. 

The  mesencephalon  has  four  surfaces :  a  dorsal,  a  ventral, 
and  two  lateral.  The  dorsal  surface  (Figs.  1  and  10),  which, 
in  the  complete  encephalon,  lies  just  ventral  to  the  posterior 
extremity  of  the  corpus  callosum  and  anterior  to  the  ventral 
incisure  of  the  cerebellum,  consists  of  two  pairs  of  rounded 
bodies  known  collectively  as  the  corpora  quadrigemina,  each 
body  individually  being  called  a  colliculus.  The  two  posterior 
(inferior)  colliculi  (colliculi  inferiores)  are  the  smaller,  and 
are  on  a  plane  ventral  as  well  as  posterior  to  the  anterior 
(superior)  colliculi  (colliculi  superiores).  These  four  bodies 
are  separated  from  each  other  by  a  crucial  sulcus ;  the  longi- 
tudinal arm  of  this  groove  terminates  behind  on  the  anterior 
medullary  velum,  its  edges  here  forming  the  frenulum  veli. 
J^iach  colliculus  has  running  forward  and  lateralward  from  it  a 
ridge  connecting  the  mesencephalon  with  the  diencephalon ; 
the  ridge  from  the  anterior  colliculus  is  called  the  anterior 
(superior)  arm  (braehium  quadrigeminum  superius),  and  that 
from  the  posterior  colliculus  is  the  posterior  (inferior)  arm 
(braehium  quadrigeminum  inferius).  The  brachia  are  sepa- 
rated by  an  interbrachial  sulcus  (sulcus  interbrachialis). . 

The  ventral  surface  (Fig.  6)  presents  two  large  rounded 
cords  emerging  from  the  pons  Varolii :  the  cerebral  peduncles 
(pedunculi  cerebri).  These  diverge  from  each  other  to  dis- 
.appear  under  the  diencephalon  after  a  course  of  about  half 
an  inch.  The  triangular  depression  left  between  them  is  the 
interpeduncular  fossa  (fossa  interpeduncularis),  in  the  bottom 
of  which  is  a  thin  lamella  of  nervous  tissue  containing  many 
foramina:  the  posterior  perforated  substance  (substantia  per- 
forata posterior).    The  foramina  are  produced  by  blood-vessels, 


THE    SUEFACE   AXATOMY   OF    THE    ENCEPHALOX.  19 

wliicli  pierce  the  lamella  and  are  pulled  out  wlien  the  pia  mater 
is  removed.  Through  the  fossa  the  third  pair  of  cranial  nerves 
makes  its  escape  from  the  mesencephalon. 

The  lateral  surface  is  marked  by  a  longitudinal  sulcus, — 
the  sulcus  lateralis, — which  indicates  the  separation  of  the 
quadrigeminal  from  the  peduncular  portion  of  the  mesen- 
cephalon. 

The  cavity  of  the  mesencephalon  is  the  aqueduct  of  Syl- 
vius (aquaeductus  cerebri),  opening  behind  into  the  fourth,  and 
in  front  into  the  third  ventricle. 


THE    SURFACE    AXATOMY    OF    THE    DIESTCEPHALOX. 

The  diencephalon  is  divided  into  the  thalamencephalon 
and  the  hypothalamus.  The  neural  canal  here  is  the  third 
ventricle. 

The  Thalamexcephalox. — The  thalamencephalon  (Fig. 
10)  is  subdivided  on  each  side  of  the  median  line  into  the  thala- 
mus, the  metathalamus,  and  the  epithalamus. 

Tlie  Thalamus. — This  is  an  elongated  oval  mass  of  gray 
matter  having  four  surfaces:  dorsal,  ventral,  lateral,  and 
medial;    and  two  extremities:    anterior  and  posterior. 

The  dorsal  surface  is  marked  by  an  obliquely  lateral  an- 
tero-posterior  groove,  the  chorioid  sulcus,  in  which  lies,  as  we 
shall  see  hereafter,  the  chorioid  plexus  of  the  lateral  ventricle. 
At  its  line  of  junction  with  the  medial  surface  is  a  narrow 
white  band, — the  stria  medullaris, — which  can  be  traced  back- 
ward to  a  small  triangular  swelling:  the  trigonum  habenulse. 
Laterally  the  dorsal  surface  is  separated  from  another  gray 
mass, — the  caudate  nucleus  of  the  corpus  striatum  of  the  telen- 
cephalon,— by  a  groove  which  lodges  a  vein, — the  vena  ter- 
minalis, — and  a  small  bundle  of  fibres :  the  stria  terminalis. 

The  medial  surface  (Fig.  8)  forms  the  lateral  wall  of  the 
third  ventricle.  It  is  marked  by  an  antero-posterior  sulcus, — 
the  sulcus  of  Monro  (sulcus  hypothalamicus), — which  indi- 
cates the  division  of  the  thalamus  from  the  hypothalamus. 
The  lateral  surface  of  the  thalamus  is  fused  with  the  telen- 
cephalon ;  the  ventral  surface  with  the  hypothalamus  and  with 
the  mesencephalon  behind.     The  anterior  extremity  of  the 


20 


THE  axato:mt  of  the  braix. 


thalamus  is  tlie  smaller;    its  most  prominent  portion  is  called 
tlie  anterior  tubercle  (tubercnlum  anterius). 

The  posterior  extremity  projects  backward,  and  lateral- 
ward  so  as  to  overhang  the  neighboring  part  of  the  mesen- 
cephalon; this  projecting  portion  is  called  the  pulvinar.  On 
its  ventral  aspect  the  posterior  extremity  is  continuous  with 
a  white  cord, — the  optic  tract  (tractus  opticus), — ^which  can 
be  traced  winding  forward,  first  lateral  and  then  ventral  to  the 
cerebral  peduncle,  and  then  medialward  into  the  postero-lateral 
angle  of  a  square  white  body, — the  optic  chiasm  (chiasma  op- 


Fig.  11. — A.  p.  c,  Anterior  peduncle  of  the  cerebellum.  C.  g..  m.,  Corpus 
geniculatum  mediale.  C.  g.  L.,  Corpus  genieulatum  laterale.  B.  F.,  Base 
of  the  peduncle  of  the  cerebrum.  Op.  tr.,  Optic  tract.  Op.  cJi.,  Optic  diiasm. 
PuJv.,  Pulvinar  of  the  thalamus.     (After  Gegenbauer.) 


ticum), — from  the  antero-lateral  angle  of  which  another  white 
cord — the  optic  nerve — ^proceeds  forward  and  lateralward. 

The  Jletathcdamus. — The  metathalamus  (Fig.  11)  con- 
sists of  the  two  geniculate  bodies,  lateral  and  medial  (corpus 
geniculatum  laterale;  corpus  geniculatum  mediale).  -These 
are  two  small  oval  bodies  which  lie  ventral  to  the  posterior 
extremity  of  the  thalamus.  The  corpus  geniculatum  laterale 
is  situated  on  the  course  of  the  optic  tract,  and  is  connected 
with  the  anterior  arm  (brachium  quadrigeminum  superius)  of 


THE    SURFACE    AXATOMY    OF    THE    EXCEPHALOX.  21 

tlie  mesenceplialon;  the  corpus  genicuktmn  mediale  is  found 
at  the  lateral  end  of  the  interbrachial  sulcus,  and  is  connected 
with  the  posterior  arm  (brachium  quadrigeminum  inferius). 

TheEpithalamus. — The  epithalamus  (Fig.  10)  comprises 
the  pineal  body  (corpus  pineale)  and  the  region  of  the  haben- 
ula.  The  pineal  body  is  a  small  flattened  oval  mass  somewhat 
reddish  in  color,  and  about  one-quarter  of  an  inch  in  diameter; 
it  rests  in  the  median  line  on  the  anterior  (superior)  collicuH 
of  the  mesencephalon.  From  its  anterior  aspect  there  runs  on 
each  side  a  slender  cord,  the  peduncle  of  the  pineal  body, 
forward  to  the  habenula.  To  the  unaided  eye  the  peduncle 
of  the  pineal  body  and  the  habenula  seem  to  be  one  and  the 
same  structure,  mth  the  trigonum  as  a  swelling  on  it ;  but,  as 
it  is  known  that  the  peduncles  connect  the  trigonum  of  one 
side  with  that  of  the  other  side,  they  are  called  the  commissure 
of  the  habenulse  (commissura  habenularum). 

The  Thied  Yextricle. — The  third  ventricle  (ventriculus 
tertius)  is  the  neural  canal  in  the  diencephalon,  which  exists 
here  as  a  narrow  space  between  the  medial  surfaces  of  the  two 
thalami,  the  latter  constituting  its  lateral  walls.  Its  anterior 
boundary  is  furnished  by  the  anterior  pillars  of  the  fornix  and 
by  the  anterior  commissure  of  the  cerebrum.  These  struct- 
ures are  parts  of  the  telencephalon,  and  will  be  described  in 
the  appropriate  place.  The  pillars  of  the  fornix  show  here  as 
two  white  cords  running  toward  the  ventral  surface  of  the 
encephalon;  they  diverge  in  their  course  and  allow  the  an- 
terior commissure  in  front  of  them  to  come  into  view.  The 
posterior  boundary  is  a  transverse  bundle  of  fibres:  the  pos- 
terior commissure  (commissura  posterior).  Passing  between 
the  adjacent  surfaces  of  the  thalami  about  the  middle  of  the 
ventricle  is  a  delicate  gray  layer,  formerly  called  the  middle 
commissure,  but  now  known  as  the  massa  intermedia. 

The  roof  of  the  ventricle  is  an  epithelial  structure.  The 
dorsal  wall  of  the  embryonic  diencejDhalon  between  the  striae 
medullares'  remains  undeveloped,  and  stretches  between  these 
as  a  layer  of  epithelial  cells.  This  epithelium,  however,  is  ad- 
herent to  a  fold  of  pia  mater  interposed  between  the  dien- 
cephalon and  the  telencephalon:  the  tela  chorioidea  of  the 
third  ventricle  hereafter  to  be  described,  which  is  often  con- 


22  THE    AXATOMY    OF    THE    BEAIX. 

sidered  tlie  actual  roof.  The  floor  of  tlie  ventricle  is  formed 
by  the  hypothalamus. 

The  Hypothalamus. — The  hypothalamus  (Figs.  6  and 
8),  when  examined  from  before  backward,  presents  the  follow- 
ing appearances : — 

If,  with  the  brain  inverted,  one  lifts  up  the  optic  chiasm, 
there  is  seen  in  the  median  line  a  sheet  of  nervous  matter :  the 
terminal  plate  (lamina  terminalis).  Posterior  and  ventral  to 
this  is  the  square  mass  of  the  optic  chiasm,  with  the  optic  nerve 
entering  it  on  each  side  in  front  and  the  optic  tract  leaving  it 
on  each  side  behind.  Behind  the  chiasm  is  a  dark  swelling, 
the  tuber  cinereum,  from  the  ventral  surface  of  which  runs 
a  slender  tube:  the  infundibulum.  The  latter  terminates  in 
an  oblong  mass  about  one-half  inch  in  diameter :  the  pituitary 
body  (hypophysis).  The  hypophysis  rests  in  the  sella  Turcica 
of  the  sphenoid  bone ;  it  consists  of  two  portions,  or  lobes,  the 
anterior  of  which  is  the  larger.  Behind  the- tuber  cinereum  on 
each  side  is  a  small,  shining,  rounded  body:  the  mamillary 
body  (corpus  mamillare). 

If  a  sagittal  section  be  made  through  the  diencephalon 
(Fig.  8),  it  will  be  noticed  that  the  floor  of  the  third  ventricle 
is  considerably  depressed  in  front,  and  that  the  bottom  of  this 
depressed  portion  is  thrown  up  into  a  transverse  ridge  by  the 
optic  chiasm.  In  this  way  there  are  produced  two  small  de- 
pressions by  the  chiasm:  one  in  front,— the  optic  recess  (re- 
cessus  opticus),  whose  anterior  wall  is  the  lamina  terminalis; 
and  the  other  behind, — the  recess  of  the  infundibulum  (re- 
cessus  infundibuli),  whose  post-erior  wall  is  the  tuber  cine- 
reum. The  recess  of  the  infundibulum  leads  into  the  inf undibr 
ulum,  which,  it  is  now  seen,  is  hollow.  Roughly  speaking, 
only  that  portion  of  the  hypothalamus  which  lies  behind  the 
infundibidum  belongs  to  the  diencephalon;  it  is  called  the 
mamillary  portion  of  the  hypothalamus  (pars  mamillaris  hypo- 
thalami). The  remainder  of  the  hypothalamus  is  the  ventral 
part  of  the  telencephalon,  and  is  called  the  optic  portion  of 
the  hypothalamus  (pars  optica  hypothalami).  For  the  sake 
of  convenience  they  have  been  described  together  here. 


THE    SURFACE    ANATOMY    OF    THE    EXCEFHALOX. 


23 


^^l"'^-    Sp.    S.posh. 


S.interp- 


B.ctnt.ascoX 


S.tenw. 


<5.7cmp.7n. 


Fig.  12." — Scheme  of  convolutions  of  lateral  surface  of  cerebral  hemisphere 
(after  Van  Gehuchten).  H.  fr.  s.,  Superior  frontal  sulcus.  S.  proBC,  Pre- 
central  sulcus.  8.  R.,  Central  sulcus  of  Rolando.  S.  poste.,  Post-central  sul- 
cus. S.  interp.,  Interparietal  sulcus.  S.  p.o.,  Parieto-occipital  fissure.  Ram. 
post.  S.,  Posterior  ramus  of  fissure  of  Sylvius.  S.  temp,  m.,  Middle  temporal 
sulcus.  S.  tem,p.  s.,  Superior  temporal  sulcus.  F.  8.,  Fissure  of  Sylvius. 
R.  ant.  asc.  8.,  Ascending  anterior  ramus  of  fissure  of  Sylvius.  R.  a. 
h.  8.,  Horizontal  anterior  ramus  of  fissure  of  Sylvius.  8.  fr.  inf.,  Inferior 
frontal  sulcus. 


24  THE    ANATOMY    OF    THE    BEAIN. 

THE    SURFACE    ANATOMY    OF    THE    TELENCEPHALON. 

As  a  result  of  the  rapid  growth  undergone  by  the  lateral 
portion  of  the  telencephalon  in  early  foetal  life,  that  vesicle  is 
greatly  elevated  on  each  side  of  the  median  line;  there  is  thus 
formed  a  deep  sulcus  separating  the  lateral  portions  from  one 
another.  This  condition  is  maintained  during  subsequent  de- 
velopment ;  so  that  in  the  fully  developed  encephalon  we  find 
two  more  or  less  symmetrical  halves,— the  hemispheres  (hem- 
isphseria), — separated  by  a  longitudinal  fissure  (fissura  longi- 
tudinalis  cerebri).  This  fissure  is  complete  in  front  and  be- 
hind, but  for  its  middle  two-fourths  is  interrupted  ventrally 
by  a  white  body:   the  corpus  callosum. 

The  Hemisphere. — Embryologically  each  hemisphere 
may  be  divided  into  the  pallium,  or  the  superficial  gray  matter, 
and  the  white  matter  directly  connected  therewith;  the  rhi- 
nencephalon,  or  the  central  olfactory  apparatus;  and  the 
corpus  striatum;  but  for  the  purpose  of  this  book  it  is  more 
convenient  to  first  consider  the  hemispheres  as  a  whole,  giving 
attention  to  its  separate  parts  later. 

The  hemisphere  is  ovoid  in  shape.  It  has  two  surfaces, — 
one  lateral  and  one  medial, — and  two  extremities, — the  an- 
terior, or  frontal,  pole  (polus  frontalis) ;  and  the  posterior,  or 
occipital,  pole  (polus  occipitalis). 

The  lateral  surface  (f acies  lateralis)  is  convex ;  it  is  folded 
in  such  a  way  as  to  present  numerous  eminences  called  con- 
volutions (gyri)  separated  by  gTooves  called  sulci.  Certain 
of  the  sulci  are  large  and  deep,  and  fairly  constant,  so  that 
they  may  be  taken  as  boundaries  by  which  to  divide  the  hemi- 
sphere on  its  lateral  surface  into  portions  called  lobes  (lobi). 
Such  sulci  are  commonly  called  fissures,  but  in  the  new  nomen- 
clature that  term  is  applied  only  to  such  sulci  as  produce  cor- 
responding elevations  in  the  cavity  of  the  hemisphere.  The 
most  prominent  of  the  fissures  is  the  fissure  of  Sylvius 
(fissura  cerebri  lateralis),  which  may  be  located  in  the  follow- 
ing way : — 

On  the  ventral  aspect  of  the  telencephalon  lateral  to  the 
optic  chiasm  there  is  found  a  lamina  of  nervous  matter  per- 
forated by  many  foramina  for  blood-vessels:   the  anterior  per- 


THE    SURFACE    ANATOMY    OF    THE    ENCEPHALO^^.  25 

f  orated  substance.  Just  lateral  to  this  substance  the  fissure  of 
Sylvius  begins;  whence  it  proceeds  lateralward  to  gain  the 
lateral  surface  of  the  hemisphere,  where  it  divides  into  three 
branches  (Fig.  12).  The  longest  of  these,  the  ramus  posterior, 
runs  dorsalward  and  backward,  to  become  gradually  lost  upon 
the  lateral  surface;  the  other  two  are  both  short  and  both 
anterior,  the  one  running  nearly  vertically  dorsalward  and 
called  the  ramus  anterior  ascendens,  the  other  running  nearly 
horizontally  forward  and  called  the  ramus  anterior  horizontalis. 

A  second  fissure  is  the  so-called  fissure  of  Rolando  (sulcus 
centralis).  It  begins  on  the  lateral  surface  near  the  longitudi- 
nal fissure  at  a  point  a  little  behind  the  junction  of  the  anterior 
with  the  posterior  half  of  the  hemisphere,  and  proceeds  for- 
ward and  ventralward  nearly  to  the  posterior  ramus  of  the 
fissure  of  Sylvius. 

A  third  fissure  is  the  parieto-occipital  (fissura  parieto- 
occipitalis).  It  begiils  on  the  medial  surface  of  the  hemisphere 
behind  the  posterior  extremity  of  the  corpus  callosum,  and 
passes  dorsalward  and  slightly  backward  to  reach  the  lateral 
surface,  where  it  disappears  after  a  forward  and  ventralward 
course  of  about  half  an  inch.  This  latter  part  is  frequently 
called  the  lateral  limb  of  the  fissure,  the  part  on  the  medial 
surface  being  the  medial  limb. 

By  means  of  the  fissures  mentioned  the  lateral  surface  is 
divided  into  five  lobes.  That  portion  which  lies  dorsal  to  the 
fissure  of  Sylvius  and  anterior  to  the  central  sulcus  of  Eolando 
is  called  the  frontal  lobe  (lobus  frontalis) ;  that  ventral  to  the 
posterior  ramus  of  the  fissure  of  Sylvius  the  temporal  lobe 
(lobus  temporalis);  that  bounded  ventrally  by  the  posterior 
ramus  of  the  fissure  of  Sylvius,  in  front  by  the  central  sulcus 
of  Rolando,  and  behind  by  the  lateral  limb  of  the  parieto-occip- 
ital fissure  the  parietal  lobe  (lobus  parietalis) ;  while  the  por- 
tion posterior  to  the  lateral  limb  of  the  parieto-occipital  fissure 
is  the  occipital  lobe.  The  fifth  division  is  the  island  of  Reil 
(insula).  This  is  found  in  the  depths  of  the  fissure  of  Sylvius 
where  that  fissure  is  dividing  into  its  rami.  The  island  can 
be  brought  into  view  by  drawing  aside  the  neighboring  over- 
hanging convolutions,  which  collectively  are  called  the  oper- 
culum.   It  will  be  observed  that  this  division  into  lobes  is  far 


26  THE   ANATOMY    OF    THE    BEAIN. 

from  complete,  since,  except  in  tke  case  of  tlie  island  of  Keil, 
eacli  lobe  is  connected  -.vitli  its  neighbors  bj  convolutions  pass- 
ing between  them,  whicli  for  this  reason  are  called  gyri  tran- 
sitivi.  This  statement  is  especially  true  of  the  parietal  and 
occipital  lobes,  between  which  there  is  scarcely  any  well- 
marked  boundary. 

Each  lobe  is  divided  into  several  convolutions  by  sulci  as 
follows:  The  frontal  lobe  is  marked  by  a  sulcus,  often  atyp- 
ical, running  parallel  with  and  anterior  to  the  central  sulcus 
of  Eolando, — the  ascending  frontal,  or  precentral,  sulcus  (sul- 
cus prsecentralis), — cutting  off  between  itself  and  the  sulcus 
of  Eolando  a  large  convolution:  the  ascending  frontal  or  an- 
terior central  convolution  (gyrus  centralis  anterior).  From 
the  precentral  sulcus  there  proceed  forward  two  other  smaller 
sulci,  the  dorsal,  or  superior  (sulcus  frontalis  superior),  and 
the  ventral,  or  inferior,  frontal  sulcus  (sulcus  frontalis  in- 
ferior), toward  the  frontal  pole;  these  divide  the  remainder 
of  the  frontal  lobe  into  three  convolutions:  the  dorsal,  or 
superior ;  the  middle ;  and  the  ventral,  or  inferior,  frontal  con- 
volutions (gyrus  frontalis  superior,  medius,  et  inferior).  The 
ventral  frontal  convolution  at  its  ventral  margin  is  divided  into 
three  parts  by  the  indentations  of  the  anterior  rami  of  the  fis- 
sure of  Sylvius:  the  posterior  division,  behind  the  ascending 
ramus,  is  the  pars  opercularis;  the  middle,  between  the  rami, 
is  the  pars  angularis;  and  the  anterior  division  is  the  pars 
orbitalis.  In  the  course  of  development  the  anterior  extremi- 
ties of  these  three  frontal  convolutions  are  bent  forward  and 
ventralward,  and  then  backward;"  so  that  they  come  to  lie  upon 
the  orbital  plate  of  the  frontal  bone  (Fig.  13),  in  which  situa- 
tion they  are  called  orbital  convolutions  (gyri  orbitales).  The 
dorsal  frontal  here  becomes  the  medial  orbital,  the  middle 
frontal  becomes  the  anterior  orbital,  and  the  ventral  frontal 
becomes  the  posterior  orbital  convolution.  The  medial  or- 
bital convolution  borders  on  the  anterior  extremity  of  the 
longitudinal  fissure,  and  contains  an  antero-posterior  groove, 
— the  olfactory  sulcus, — which  lodges  a  white  band, — the  ol- 
factory tract ;  the  portion  of  the  gyrus  medial  to  this  sulcus  is 
known  as  the  straight  convolution  (gyrus  rectus). 

The  parietal  lobe  contains  a  fairly-constant  sulcus,  the 


THE    SUEFACE   AXATOJIY    OF    THE    EXCEPHALOX.  27 


Su2.pl/ 


Fig.  13. — Scheme  of  convolutions  of  ventral  aspect  of  eei-ebral  hemisphere 
(after  Van  Gehuchten).  Eul.  oJf.,  Olfactory  sulcus.  Siil.  temp,  inf.,  Inferior 
temporal  sulcus.     Fis.  col.,  Collateral  fissure. 


28  THE    AIv^ATOMY    OF    THE    BEAIN. 

interparietal  (snlciTS  interparietalis),  by  means  of  which  it  is 
divided  into  three  convolntions.  This  sulcus  begins  near  the 
posterior  ramus  of  the  fissure  of  Sylvius,  and  first  runs  parallel 
with  the  fissure  of  Kolando,  and  then  turns  backward  to  termi- 
nate near  or  in  the  occipital  lobe.  As  it  makes  its  backward 
turn  it  gives  off  an  ascending  branch,  which  is  sometimes  an 
independent  sulcus^, — the  postcentral  (sulcus  postcentralis), — - 
which  continues  the  course  of  t\e  parent-sulcus  dorsalward. 
The  long  convolution  lying  between  this  latter  sulcus  and  the 
interparietal  behind,  and  the  central  sulcus  of  Eolando  in  front 
is  the  ascending  parietal,  or  posterior  central,  convolution 
(gyrus  centralis  posterior).  That  portion  of  the  lobe  con- 
tained between  the  posterior  part  of  the  interparietal  sulcus 
and  the  longitudinal  fissure  is  the  dorsal,  or  superior,  parietal 
lobule  (lobulus  parietalis  superior).  The  remainder  of  the 
lobe  ventral  and  posterior  to  the  interpiarietal  sulcus  is  the 
ventral,  or  inferior,  parietal  lobule  (lobulus  parietalis  inferior) ; 
its  anterior  portion  bordering  the  posterior  ramus  of  the  fis- 
sure of  Sylvius  is  often  termed  the  supramarginal  convolu- 
tion (gyrus  supramarginalis)  while  the  posterior  part  is  called 
the  angular  convolution  (gyrus  angularis). 

The  temporal  lobe  is  divided  into  five  convolutions  as 
follows:  The  portion  adjacent  to  the  posterior  ramus  of  the 
fissure  of  Sylvius  is  the  dorsal,  ar  superior,  temporal  con- 
volution (gyrus  temporalis  superior).  It  is  separated  by.  an 
antero-posterior  sulcus, — the  dorsal,  or  superior,  temporal  sul- 
cus (sulcus  temporalis  superior), — from  the  middle  temporal 
convolution  (gyrus  temporalis  medius).  The  latter  convolu- 
tion is  separated  by  another  antero-posterior  sulcus,  the  middle 
temporal  sulcus  (sulcus  temporalis  medius),  from  the  ventral, 
or  inferior,  temporal  convolution  (gyrus  temporalis  inferior). 
The  last  two  convolutions  are  especially  badly  defined.  At 
this  point  the  lobe  makes  a  ventral  bend  toward  the  median 
line,  so  as  to  present  upon  the  ventral  aspect  of  the  enceph- 
alon.  Here  we  find  two  convolutions  (Figs.  13  and  14). 
The  first  is  large  and  spindle-shaped,  the  fusiform  convolu- 
tion (gyrus  fusiformis),  and  is  limited  laterally  by  the  ven- 
tral, or  inferior,  temporal  sulcus  (sulcus  temporalis  inferior). 
On  its  medial  side  it  is  bounded  by  a  long  fissure  extending 


THE    SUEFACE    AXATOMY    OF    THE    EXCEPHALOX. 


29 


5ul.  C.C. 


SlJlma!''J 


Sid  sub f' 


Sulsuhp 


,^^Sulcal.7vaiy. 


2^73.  Ce?k. 


Fig.  14. — Scheme  of  convolutions  on  medial  surface  of  cerebral  hemisphere 
(after  Van  Gehuchten).  Fis.  S.,  Fissure  of  Sylvius.  Sul.  cal.  marg.,  Calloso- 
marginal  sulcus.  Sul.  subf.,  Subfrontal  sulcus.  Sul.  C.  C,  Sulcus  of  corpus 
callosum.  Sill,  marg.,  Marginal  sulcus.  Sul.  subp.,  Subparietal  sulcus. 
Fis.  P.O.,  Parieto-occipital  fissure.  Fis.  calc,  Calcarine  fissure.  Fis.  den.. 
Dentate  fissure.    Fis.  col..  Collateral  fissure. 


30  THE   AXATOMY    OF    THE    BEAIN. 

almost  to  the  anterior  extremity  of  tlie  lobe,  the  collateral 
fissure  (fissura  collateralis),  medial  to  the  posterior  part  of 
which  is  the  lingual  convolution  (gyrus  lingualis). 

The  occipital  lobe  may  be  roughly  divided  into  three 
convolutions:  dorsal,  or  superior;  middle;  and  ventral,  or 
inferior.  Some  make  only  two  divisions  of  this  lobe,  with 
several  small  convolutions  in  each  division;  in  this  case  the 
dorsal  division  is  composed  of  the  gyri  occipitales  superiores, 
and  the  ventral  of  the  gyri  occipitales  laterales. 

The  island  of  Eeil  contains  three  convolutions  surrounded 
by  a  circular  sulcus  (sulcus  circularis).  This  lobe,  as  we  have 
seen,  is  overhung  by  the  neighboring  convolutions,  which 
collectively  constitute  the  operculum.  As  the  operculum  is 
furnished  by  the  frontal,  parietal,  and  temporal  lobes,  there 
is  a  pars  frontalis,  a  pars  parietalis,  and  a  pars  temporalis 
operculi. 

The  medial  surface  (facies  medialis)  of  the  hemisphere 
(Fig.  14)  is  convoluted  like  the  lateral  surface,  but  its  con- 
volutions are,  as  a  rule,  larger  and  less  complex  in  arrange- 
ment. As  limits  for  these  convolutions  we  have,  first,  the 
medial  limb  of  the  parieto-occipital  fissure;  beginning  at  the 
ventral  extremity  of  this  fissure  and  running  backward  usu- 
ally to  the  posterior  extremity  of  the  hemisphere  is  the  cal- 
carine  fissure  (fissura  calcarina),  included  between  which  and 
the  parieto-occipital  fissure  is  a  wedge-shaped  convolution,  the 
cuneus.  Ventral  to  the  calcarine  fissure  is  the  lingual  con- 
volution already  described  as  a  part  of  the  temporal  lobe. 
This  convolution  is  continuous  in  front  Avith  a  narrow  con- 
volution hmited  ventrally  by  the  collateral  fissure,  the  hippo- 
campal  convolution  (gyrus  hippocampi),  the  anterior  extrem- 
ity of  which  is  recurved  so  as  to  resemble  a  hook,  and  which, 
therefore,  is  known  as  the  uncus.  The  hippocampal  convolu- 
tion is  limited  dorsally  by  the  dentate  fissure  (fisslira  hippo- 
campi), which  begins  just  ventral  to  the  posterior  extremity 
of  the  corpus  callosum,  and  curves  forward  and  ventralward 
nearly  to  the  uncus.  In  the  luiddle  of  the  medial  surface  is 
seen  the  sagittal  section  of  the  corpus  callosum.  It  is  sepa- 
rated from  the  adjacent  convolutions  by  a  sulcus, — the  sulcus 
of  the  corpus  callosum  (sulcus  corporis  callosi), — which,  be- 


THE    SUEFACE   AXATOMY    OF   THE    ENCEPHALON". 


31. 


lr)p.ch/optn 


Fig.  15.— OZ.  b.,  Olfactory  bulb.  01.  tr.,  Olfactory  tract.  R.,  Rostrum  of 
corpus  callosum.  L.  f.,  Longitudinal  fissure.  P.  a.,  Parolfactory  area.  Trig., 
Olfactory  trigonum.  M.  St.,  Medial  stria.  Ant.  com.,  Region  of  anterior  com- 
missure. L.  t..  Lamina  terminalis.  Op.  cJi.,  Optic  chiasm.  Op.  tr.,  Optic 
tract.  G.  s..  Gyrus  subcallosus.  A.  p.  s.,  Anterior  perforated  substance. 
L.  St.,  Lateral  stria.   (After  His.) 


32  THE    AXATOilY    OF    THE    BEAIX. 

ginning  ventral  to  tlie  anterior  extremity  of  tliat  body,  arches 
backward  over  its  dorsal  surface  to  terminate  behind  its  poste- 
rior extremity  by  opening  into  the  dentate  fissure.  Begin- 
ning in  front  of  the  anterior  extremity  of  the  corpus  callosum 
is  the  calloso-marginal  sulcus  (sulcus  cinguli),  which  winds 
dorsalward  and  backward  to  a  point  dorsal  to  the  posterior 
extremity  of  the  corpus  callosum;  about  the  middle  of  its 
course  it  sends  off  an  ascending  branch, — the  subfrontal  sul- 
cus (sulcus  subfrontalis), — and  near  its  termination  another 
ascending  branch:  the  marginal  sulcus  (sulcus  marginalis). 
The  portion  of  the  hemisphere  cut  off  dorsal  to  the  calloso- 
marginal  sulcus  is  often  called  the  calloso-marginal  convolu- 
tion; it  will  be  noticed  that  it  is  merely  the  medial  surface 
of  the  dorsal,  or  superior  frontal,  convolution.  Between  the 
subfrontal  sulcus  in  front  and  the  marginal  sulcus  behind  is 
the  paracentral  lobule  (lobulus  paracentralis),  which  is  the 
combined  medial  surfaces  of  the  anterior  and  posterior  cen- 
tral gyri.  The  calloso-marginal  sulcus  (sulcus  cinguli)  is 
sometimes  continued  backward  nearly  to  the  parieto-occipital 
fissure,  and  this  part  of  it  is  called  the  subparietal  sulcus  (sid- 
cus  subparietalis).  Between  it,  ventrally,  the  parieto-occipital 
fissure  behind,  and  the  marginal  sulcus  in  front,  is  a  large 
square  convolution:  the  prsecuneus.  BetAveen  the  sulcus  of 
the  corpus  callosum  ventrally  and  the  calloso-marginal  sulcus 
dorsally  is  a  long,  narrow  convolution:  the  convolution  of 
the  corpus,  callosum.  It  will  be  seen  that  this  is  continuous 
with  the  hippocampal  convolution  around  the  posterior  ex- 
tremity of  the  corpus  callosum."  These  two  convolutions  to- 
gether have  been  called  the  limbic  lobe  of  Broca;  in  the 
nomenclature  now  employed  they  constitute  the  gyrus  forni- 
catus,  divided  into  two  parts, — the  gyrus  cinguli,  correspond- 
ing to  what  was  called  the  convolution  of  the  corpus  callosum, 
and  the  gyrus  hippocampi, — while  their  point  of  union  around 
the  posterior  extremity  of  the  corpus  callosum  is  the  isthmus 
gyri  fornicati. 

The  R]ihiencepliaIo7i. — The  rhinencephalon  (Tig.  15)  is 
developed  as  an  offshoot  from  the  anterior  ventral  portion  of 
the  telencephalon.  The  medial  orbital  convolution,  as  we 
have  seen,  contains  an  antero-posterior  sulcus  parallel  to  the 


THE    SURFACE    AXxVTOMY    OF    THE    EXCEPHALOX.  33 

anterior  extremity  of  tlie  longitudinal  fissure:  the  olfactory 
sulcus  (sulcus  olfactorius).  In  this  lies  a  white  band,  the 
olfactory  tract  (tractus  olfactorius),  which,  when  followed 
forward,  is  seen  to  emerge  from  a  small  oval  enlargement: 
the  olfactory  bulb  (bulbus  olfactorius).  Behind,  at  the  edge 
of  the  orbital  convolution,  the  tract  develops  a  small  tri- 
angular swelling:  the  olfactory  triangle  (trigonum  olfac- 
torium).  From  this  triangle  set  out  two  small  cords:  the 
olfactory  roots,  or  striae.  The  medial  root  (stria  olfactoria 
medialis)  runs  backward  toward  the  median  line,  to  enter  a 
small  gray  area:  the  olfactory  area  of  Broca  (area  parolfac- 
toria).  The  lateral  root  (stria  olfactoria  lateralis)  runs  back- 
ward and  lateralward  to  enter  the  anterior  extremity  of  the 
hippocampal  convolution.  In  its  course  it  crosses  the  ante- 
rior perforated  substance  (substantia  perforata  anterior):  a 
thin,  gray  lamella  containing  numerous  foramina  for  vessels. 
Limiting  this  lamella  medially  and  behind  is  a  narrow  white 
cord  running  between  the  anterior  extremity  of  the  corpus 
callosum  and  the  hippocampal  convolution;  it  has  been  called 
the  j)eduncle  of  the  corpus  callosum,  but  it  is  more  in  accord 
with  our  present  knowledge  to  regard  it  as  a  convolution, 
called,  from  its  position,  the  gyrus  subcallosus.  By  its  means 
the  two  anterior  extremities  of  the  limbic  lobe,  or  gyrus 
fornicatus,  are  connected. 

It  is  customary  to  divide  the  rhinencephalon  into  two 
portions:  an  anterior  (pars  anterior)  and  a  posterior  (pars 
posterior).  The  former  contains  the  bulb,  the  tract,  the  tri- 
angle, the  medial  stria,  and  the  area  parolf actoria ;  the  latter 
the  perforated  substance,  the  lateral  stria,  and  the  gyrus 
subcallosus. 

The  Vextral  Portiox  of  the  Telexcephalox. — The 
divisions  of  the  telencephalon  which  we  have  been  studying 
are  all  developed  from  that  part  of  the  embryonic  vesicle 
which  lies  dorsal  to  the  neural  cavity.  The  ventral  portion 
of  the  telencephalon  produces  the  optic  part  of  the  hypo- 
thalamus (pars  optica  hypothalami);  this  has  already  been 
described  in  the  account  given  of  the  diencephalon. 


CHAPTEE  III. 

The  Ixteexal  Anatomy  of  the  Excephalon. 

the  ixteexal  axatomy  of  the  tiiyelexcephalox. 

Ix  tracing  the  continuity  of  stnictnre  between  the  me- 
dulla oblongata  and  the  spinal  cord  we  shall  find  that  a 
gradual,  but  marked,  rearrangement  of  both  gTaj  and  white 
matters  occurs;  moreover,  we  shall  find  structures  in  the 
medulla  which  are  lacking  in  the  cord. 

This  rearrangement  of  matter  begins  even  in  the  cord. 
If  a  section  through  the  first  cervical  segment  of  the  cord 
(Fig.  16)  be  examined,  it  will  be  noticed  that  the  dorsal  horn 
of  the  gray  matter  has  been  bent  ventro-laterally  in  such  a 
manner  as  to  describe  a  curve,  the'  concavity  of  which  is 
ventral.  The  neck  of  the  horn  is  much  thinned,  while  the 
gelatinous  substance  of  Rolando  (substantia  gelatinosa)  is 
enlarged,  and  is  capped  laterally  by  the  cross-section  of  a 
bundle  of  slender  nerve-fibres.  These  fibres  are  derived  from 
the  fifth  cranial,  or  trigeminal  t*nerve.  In  the  study  of  the 
surface  anatomy  of  the  pons  Varolii  we  have  seen  that  this 
nerve  pierces  the  ventral  surface  of  the  pons;  in  its  sub- 
stance the  sensory  fibres  of  the  nerve,  after  the  manner  of 
sensory  nerves  in  general,  bifurcate  into  ascending  and  de- 
scending branches:  the  latter  run  as  far  as  the  first  segment 
of  the  cord.  They  constitute  the  spinal  tract  of  the  trigem- 
inal nerve  (tractus  spinalis  nervi  trigemini),  the  cross-section 
of  which  appears  very  distinctly  all  through  the  posterior 
portion  of  the  pons  and  through  the  entire  extent  of  the  me- 
dulla. It  is  accompanied  by  the  gelatinous  substance,  which 
is  situated  medial  to  it,  and  is  the  terminal  nucleus  of  its 
fibres  (nucleus  tractus  spinalis  nervi  trigemini).  In  the  cer- 
vical region  of  the  cord  the  gray  matter  exhibits  the  so-called 
lateral  horn,  from  which  the  fibres  of  the  eleventh  cranial, 
or  spinal  accessorv,  nerve  arise.     This  nucleus  is  continued 

(34) 


THE    INTEEXAL    AXATOMY    OF    THE    EXCEPHALOX. 


D.pyln  "'^.h. 


Fig.  16. — D.  7/.,  Dorsal  lion.  XI,  Spinal  accessory  nerve.  F.  r.,  Formatio 
reticularis.  1.  //.,  Ventral  horn.  T.  r.  f.,  Ventral  root-fibres.  T'.,  Spinal 
tract  of  trigeminal  nerve.  Siihs.  (jcL.  Substantia  gelatinosa.  F.  G.,  Funicu- 
lus of  Goll  (funiculus  gracilis).  F.  i?., 'Funiculus  of  Burdaeli  (funiculus 
cuneatus).  C.  pij.  tr.,  Crossed  pyramidal  tract  (fasciculus  cerebro-spinalis 
lateralis).  D.  c.  tr.,  Direct  cerebellar  tract  (fasciculus  cerebello-spinalis). 
Gotv.,  Tract  of  Gowers  (fasciculus  antero-lateralis  superficialis).  L.  y.  b., 
Lateral  ground-bundle  (fasciculus  lateralis  proprius).  T.  g.  5.,  Ventral 
ground-bundle  (fasciculus  anterior  proprius).  D.  pij.  tr..  Direct  pyramidal 
tract   (fasciculus  cerebro-spinalis  anterior). 


36  THE    AXATOMY    OF    THE    BKAIX. 

into  the  posterior  part  of  the  medulla,  Avliere  it  keeps  the  same 
relative  position. 

Lateral  to  the  gray  matter  in  the  cervical  portion  of  the 
cord  appears  the  formatio  reticularis:  a  net-work  of  trans- 
verse and  longitudinal  fibres,  vhich  attains  much  fuller  de- 
velopment in  the  medulla. 

An  important  factor  in  the  rearrangement  of  the  white 
and  gray  matters  is  the  decussation  of  the  pyramids  (Fig.  17). 
The  pyramids  of  the  medulla  are  composed  of  fibres  which 
arise  in  certain  convolutions  of  the  telencephalon,  and  con- 
vey impulses  to  the  nuclei  of  origin  of  the  motor  peripheral 
nerves.  On  arriving  at  the  spinal  end  of  the  medulla  the 
great  majority  of  these  fibres  cross  the  median  line  to  the 
lateral  column  of  the  opposite  side  of  the  cord,  where  they 
form  the  crossed  pyramidal  tract  (fasciculus  cerebro-spinalis 
lateralis);  a  few  remain  uncrossed,  and  descend  in  the  ven- 
tral column  of  the  cord  as  the  direct  pyramidal  tract  (fascic- 
ulus cerebro-spinalis  anterior).  The  decussating  fibres,  cross- 
ing from  the  pyramid  of  one  side  to  the  lateral  column  of  the 
other,  pass  through  the  base  of  the  ventral  horn,  and  sever  it 
from  the  central  gray  matter.  If  we  follow  these  fibres  in 
the  opposite  direction, — i.e.,  from  the  cord  to  the  medulla, 
— it  will  be  seen  that  in  the  medulla  they  occupy  the  region 
corresponding  to  that  which  thss*  ventro-lateral  ground-bundle 
occupies  in  the  cord.  The  latter  bundle  continues  its  course 
into  the  medulla,  and  there  lies  dorsal  to  the  pyramid  and 
ventral  to  the  central  canal.  The  other  tracts  of  white  matter 
maintain  the  same  relative  positions  in  the  posterior  part  of 
the  medulla  as  in  the  cord. 

Ventral  to  the  funiculus  of  GoU  (funiculus  gracilis)  is 
a  gray  mass  continuous  with  the  dorsal  horn;  a  similar,  but 
more  rounded,  mass  is  ventral  to  the  funiculus  of  Burdach 
(funiculus  cuneatus).  As  we  follow  these  objects  through 
the  medulla  (Fig.  18),  the  gray  masses  steadily  increase  in 
size,  the  lateral  one  extending  farther  forward,  until"  they 
terminate  in  the  enlargements  which  we  have  called  the  clava 
and  the  cuneate  tubercle.  The  funiculi  of  white  matter  dor- 
sal to  them,  however,  become  gradually  thinner,  imtil  at  the 
level  of  the  clava  and  cimeate  tubercle,  respectively,  they 


THE    IXTERXAL    ANATOMY    OF    THE    EXCEPHALOX. 


37 


Tr.sp.n.Vrla 


even 


D.B 


Fig.  17. — F.  G.,  Funiculus  of  Goll.  N.  f.  G.,  Nucleus  of  the  funiculus  of 
Goll.  F.  B.,  Funiculus  of  Burdach.  N.  f.  B.,  Nucleus  of  the  funiculus  of 
Burdach.  XI,  Spinal  accessory  nerve.  Tr.  sp.  n.  trig.,  Spinal  tract  of  the 
trigeminal  nerve.  S^l'bs.  gel.,  Substantia  gelatinosa.  C.  ven.,  Ventral  horn. 
D.  P.,  Decussation  of  the  pyramids.  Ten.  gr.  huinl.,  Ventro-lateral  ground- 
bundle.      (After  Henle.) 


38  THE    ANATOMY    OF    THE    BRAIN". 

cease  altogether.  The  gray  masses,  then,  are  the  terminal 
miclei  of  the  fnniculi  of  Goll  and  BurJach  (nucleus  funiculi 
gracilis;    nucleus  funiculi  cuneati). 

]^umerous  fibres  are  seen  sweeping  across  each  half  of 
the  section  toward  the  median  line  in  curves  with  the  con- 
cavities dorsal:  the  internal  arcuate  fibres  (fibrae  arcuata^  in- 
ternae).  Thev  are  in  great  part  the  axones  of  cells  situated  in 
the  nuclei  of  the  funiculi  of  Goll  and  Burdach.  On  reach- 
ing the  median  line,  they  cross  to  the  opposite  side  and  take 
a  longitudinal  direction  forward,  occupying  the  same  region 
as  the  ventro-lateral  ground-bundle  from  the  cord,  and  with 
the  latter  form  the  prominent  tract  of  fibres  known  as  the 
medial  lemniscus  (lemniscus  medialis).  The  crossing  in  the 
median  line  of  these  arcuate  fibres  from  both  sides  constitutes 
the  decussation  of  the  lemnisci  (decussatio  lemniscorum), 
while  the  median  line  in  which  they  decussate  is  called  the 
raphe.  Since  many  of  the  fibres  of  the  lemniscus  are  derived 
from  the  terminal  nuclei  of  the  funiculi  of  Goll  and  Bur- 
dach of  the  opposite  side,  each  lemniscus  may  be  regarded  as 
the  indirect  continuation  of  these  funiculi.  Here,  then,  in 
the  posterior  part  of  the  medulla  are  two  great  decussations: 
the  ventral  one  of  motor  fibres,  the  dorsal  one  of  sensory 
fibres.  These  fibres  are  the  principal  conducting-tracts  be- 
tween the  cortex  of  the  telencephalon  and  the  peripheral 
nerves,  and  we  shall  meet  them  in  all  the  succeeding  portions 
of  the  encephalon. 

Many  of  the  internal  arcuate  fibres  are  axones  from  the 
cells  in  the  substantia  gelatinosa,  the  terminal  nucleus  of  the 
spinal  tract  of  the  trigeminal  nerve.  Tarther  forward  many 
are  likewise  derived  from  the  nuclei  of  other  sensory  cranial 
nerves.  These  arcuate  fibres  from  the  nuclei  of  sensory  nerves 
also  cross  the  raphe,  but  the  course  pursued  by  them  thereafter 
is  not  definitely  settled,  some  holding  the  opinion  that  they 
travel  in  the  medial  lemniscus,  while  others  believe  that  they 
form  separate  tracts  in  the  dorsal  part  of  the  formatio  fetic- 
idaris.  Certainlj^  some  of  them,  at  least,  join  the  lemniscus 
of  the  opposite  side  from  that  in  which  they  arise.  In  the 
case  of  the  nerve  of  hearing  we  shall  see  hereafter  that  the 
fibres  which  arise  in  its  terminal  nuclei  form  a  separate  tract. 


THE    IXTEEXAL    AXATOMY    OF    THE    EXCEPHALOX. 


39 


Int.arc.fi 


D.C.h: 

Gom 


Fig.  18. — 'Nuc.  XII,  Nucleus  of  hypoglossal  nerve.  'Nuc.  XI,  Nucleus  of 
spinal  accessory  nerve.  F.  B.,  Funiculus  of  Burdach.  Tr.  sp.  n.  trig.,  Spinal 
tract  of  trigeminal  nerve.  D.  c.  tr.,  Direct  cerebellar  tract.  Goic,  Tract  of 
Gowers.  XI,  Spinal  accessory  nerve.  PW-,  Pyramid.  XII,  Hypoglossal 
nerve.  Dec.  lem..  Decussation  of  lemniscus.  Int.  arc.  fih.,  Internal  arcuate 
fibres.  Suits,  gel.,  Substantia  gelatinosa.  K.  f.  B.,  Nucleus  of  funiculus  of 
Burdach.     ISf.  f.  G.,  Nvicleus  of  funiculus  of  GoU. 


40  THE    ANATOMY    OF    THE    BEAIlSr. 

Many  of  the  arcuate  fibres  are  derived  from  the  pyra- 
mids, crossing  the  median  line  to  reach  the  nuclei  of  origin 
of  the  motor  nerves,  and  still  others  are  fibres  connecting  the 
sensory  with  the  motor  nuclei. 

Finally  we  have  to  note  the  changes  which  occur  in  the 
central  canal.  As  the  fourth  ventricle  is  approached,  the 
diameter  of  the  canal  increases,  until  at  the  level  of  the 
termination  of  the  funiculus  of  Goll  in  its  nucleus  the  canal 
is  covered  only  by  the  thinned,  dorsal,  gray  commissure.  At 
last  the  dorsal  wall  becomes  reduced  to  its  epithelial  lining, 
which,  as  we  have  seen,  is  continuous  with  the  epithelium 
lining  the  ventral  surface  of  the  tela  chorioidea  of  the  fourth 
ventricle,  and  the  canal  is  now  said  to  have  "opened  out"  into 
the  ventricle. 

Proceeding  to  the  study  of  the  anterior  portion  of  the 
medulla,  we  begin  with  a  section  through  the  posterior  ex- 
tremity of  the  calamus  scriptorius  (Fig.  19).  The  funiculus 
of  Goll  and  its  nucleus  have  ceased  to  exist,  but  the  funiculus 
of  Burdach,  though  much  smaller  than  before,  is  still  present. 
The  semilunar  section  of  the  trigeminal  nerve  lying  lateral 
to  its  nucleus  is  a  prominent  feature.  It  will  be  noted  that 
this  tract  does  not  here  reach  the  periphery  of  the  medulla, 
but  has  lateral  to  it  a  bundle  of  oblique  fibres;  this  bundle 
is  the  direct  cerebellar  tract  froi'u  the  spinal  cord  (fasciculus 
cerebello-spinalis),  which,  having  ascended  in  the  lateral  tract 
of  the  medulla,  in  this  region  makes  a  dorsal  bend  to  enter 
the  corpus  restiforme.  The  tract  of  Gowers  (fasciculus  antero- 
laterahs  superficialis)  keeps  the  same  position  ventral  to  the 
direct  cerebellar  tract. 

Farther  ventral  is  the  section  of  the  olive,  which  here 
shows  as  three  pieces:  a  dorsal,  or  dorsal  accessory  olivary 
nucleus  (nucleus  olivaris  accessorius  dorsalis);  a  medial,  or 
medial  accessory  olivary  nucleus  (nucleus  olivaris  accessorius 
medialis);  and  a  central  portion,  or  inferior  olivary  nucleus 
(nucleus  olivaris  inferior).  The  latter  is  by  far  the  largest;, 
it  is  a  convoluted  lamina  of  gray  matter  with  an  opening,  the 
hilus,  toward  the  raphe,  through  which  pass  numerous  fibres 
which  connect  it  with  the  cerebellar  hemisphere  of  the  op- 
posite side:    the  cerebello-olivary  fibres. 


THE    INTEKXAL   AXAT05IY    OF    THE    EXCEPHALOX. 


41 


NiicXII  NuC.f^.B 


Rctad. 


KoiVP: 


Tvsp.  n .  trig. 

Subs,  gel- 
X        ^ 
D.c.tr. 

_  -Nucamh- 
Gow. 
'.int.  I  em. 


N.ao. 


PijkC.o.p. 


Fig.  19. — 'NuG.  XII,  Nucleus  of  hypoglossal  nerve.  'Nuc.  a.  c,  Nucleus  of 
ala  cinerea.  Ishic  f.  B.,  Nucleus  of  funiculus  of  Burdacli.  F.  B.,  Funiculus 
of  Burdach.  Tr.  sol.,  Tractus  solitarius.  Tr.  sp.  n.  trig..  Spinal  tract  of 
trigeminal  nerve.  Subs,  gel.,  Substantia  gelatinosa.  X,  Vagus  nerve. 
D.  C.  tr.,  Direct  cerebellar  tract.  Nuc.  ami)..  Nucleus  ambiguus.  Goio.,  Tract 
of  Gowers.  St.  int.  lem.,  Interolivary  stratum  of  lemniscus.  C.  0.  jf.,  Cere- 
bello-olivary  fibres.  Pyr.,  Pyramid.  N.  a.  0.  m.,  Medial  accessory  olivary 
nucleus.  XII,  Hypoglossal  nerve.  :N.  o.  inf.,  Inferior  olivary  nucleus. 
IV.  a.  0.  d.,  Dorsal  accessory  olivary  nucleus. 


42  THE    AXATOMY    OF    THE    BEAIX. 

On  eacli  side  of  the  ventral  median  snlcns  is  the  pyra- 
mid. Dorsal  to  the  pyramid  is  the  bundle  of  sensory  fibres 
which  farther  forward  goes  to  form  the  medial  lemniscus, 
seen  as  a  triangular  tract  between  the  olives  and  hence  known 
as  the  interolivary  layer  (stratum  interolivare  lemnisci);  the 
most  dorsal  of  the  fibres  near  the  raphe  in  this  situation  are 
continuous  farther  forward  with  the  medial  longitudinal 
bundle  (fasciculus  longitudinalis  medialis):  a  tract  of  fibres 
which  will  become  much  more  evident  as  we  proceed.  These 
fibres  correspond  to  those  of  the  ventral  ground-bundle  of 
the  spinal  cord.  In  the  floor  of  the  ventricle  are  the  nuclei 
of  some  of  the  cranial  nerves.  On  each  side  of  the  median 
line  is  a  collection  of  large  cells:  the  nucleus  of  origin  of  the 
twelfth  cranial  or  hypoglossal  nerve.  The  root-fibres  of  the 
nerve  are  conspicuous,  running  ventro-lateralward  medial  to 
the  olive  to  escape  from  the  medulla  through  the  ventro- 
lateral sulcus.  This  nucleus  consists  of  a  long  column  of  cells 
extending  from  the  level  of  the  decussation  of  the  pyramids 
nearly  to  that  of  the  strige  acusticas.  In  the  posterior  part 
of  the  medulla  the  nucleus  lies  ventro-lateral  to  the  central 
canal;  in  the  anterior  portion  it  corresponds  to  the  trigonum 
hypoglossi  in  the  floor  of  the  ventricle. 

Lateral  and  somewhat  dorsal  to  the  nucleus  of  the  twelfth 
is  the  terminal  nucleus  of  the  scaisory  portion  of  the  tenth 
cranial,  or  pneumogastric  or  vagus,  nerve  (nucleus  alse  cine- 
re^).  Most  of  the  sensory  fibres  of  the  nerve  end  in  this 
nucleus,  but  some  descend  after  the  manner  of  the  spinal 
tract  of  the  trigeminal  nerve,  forming  a  part  of  a  small  bun- 
dle dorsal  and  lateral  to  the  nucleus  of  the  ala  cinerese:  the 
tractus  solitarius.  Around  the  latter  is  a  column  of  gray 
matter  in  which  the  fibres  of  the  tract  end:  the  nucleus  of 
the  solitary  tract  (nucleus  tractus  solitarii).  These  two  nuclei 
are  really  common  to  both  the  tenth  and  the  ninth  (glosso- 
pharyngeal) cranial  nerves,  the  latter  terminating  in  their 
more  anterior  portions.  The  tractus  solitarius  consists,  in  "the 
main,  of  fibres  derived  from  the  glosso-pharyngeal  nerve. 
Moreover,  both  of  these  nerves  are  mixed  nerves:  i.e.,  they 
contain  both  motor  and  sensory  fibres.  ISTow,  the  nucleus  of 
origin  of  the  motor  fibres  is  the  nucleus  ambiguus.     The  ven- 


THE    IXTEEXAL    AXATOMY    OF    THE    EXCEniALOX. 


J3 


^^fV./:¥nL 


■--Tt~^> 


St.inf.lem, 


Pim  Ml 


Fig.  20. — Isiuc.  XII,  Nucleus  of  hypoglossal  nerve,  l^^uc.  a.  c,  Nucleus  of 
ala  cineiea.  Tr.  sol.,  Tractus  solitarius.  D.  r.  Till,  Descending  root  of 
vestibular  nerve.  C.  v.,  Corpus  restifovnie.  Tr.  sp.  T.,  Spinal  tract  of  tri- 
geminal nerve.  *S'w?>s.  gel..  Substantia  gelatinosa.  IX,  Glosso-pliaryngeal 
nerve.  A',  Vagus  nerve.  C.  0.  f.,  Cerebello-olivaiy  fibres.  Gow.,  Gowers's 
tract.  Xiic.  ami)..  Nucleus  ambiguus.  X.  a.  o.  d.,  Dorsal  accessory  olivary 
nucleus.  X.  o.  inf.,  Inferior  olivary  nucleus.  XII,  Hypoglossal  nerve.  Pyr., 
Pyramid.     St.  int.  Zem.,  Interolivary  stratum  of  the  lenmisciis. 


44 


THE   ANATOMY    OF    THE    BKAIN. 


tral  liorn  of  the  cord,  after  being  cut  off  by  tlie  decussating 
pyramid,  does  not  disappear  entirely,  but  continues  forward 
in  tbe  medulla,  to  furnish  nuclei  for  several  cranial  nerves. 
It  thus  furnishes  that  for  the  ninth  and  tenth  cranial  nerves, 
— the  nucleus  ambiguus, — which  is  located  about  midway  be- 
tween the  olive  and  the  gelatinous  substance  and  dorsal  to  a 
line  connecting  them.  Its  axones  take  a  dorso-lateral  route, 
and  join  the  sensory  fibres.  It  will  be  observed  that  the  root- 
fibres  of  these  two  nerves  run  through  the  spinal  tract  of  the 
trigeminal  nerve  and  the  gelatinous  substance. 


Ce*-6lrelln 


Fig.  21. — B.  eoft.  arc,  Dorsal  external  arcuate  fibres.  D.  c.  tr.,  Direct 
cerebellar  tract.  Y.  ext.  arc,  Ventral  external  arcuate  fibres.  (After 
Edinger.) 


The  internal  arcuate  fibres  are  very  numerous,  sweeping 
across  the  section  from  all  the  sensory  nuclei.  That  portion 
of  the  section  through  which  they  pass — between  the  floor  of 
the  ventricle,  the  medial  lemniscus,  the  inferior  olive,  and  the 
gelatinous  substance — is  the  fully-developed  formatio  reticu- 
laris of  the  medulla :  a  mixture  of  white  and  gray  matter  "be- 
lieved to  be  associational  in  function. 

The  next  section  (Fig.  20)  passes  through  all  three  of 
the  triangular  areas  into  which  the  calamus  scriptorius  is 
divided,  the  trigonum  hypoglossi  containing  the  nucleus  of 


THE    IXTEENAL    AXATOMY    OF    THE    EXCEPHALOX. 


45 


St.ac. 


m.iL 


^»-Sa6sj/e?., 


N-o-inp\ 


Fig.  22.— M.  Z.  b.,  Medial  longitudinal  bundle.  Suhs.  gel.,  Substantia 
gelatinosa.  Med.  Urn.,  Medial  lemniscus.  Pyr.,  Pyramid.  2V.  o.  int,  In- 
ferior olivary  nucleus.  2V.  «.  o.  d,  Dorsal  accessory  olivary  nucleus.  Goxc, 
Gowers's  tract.  Tr.  sp.  n.  trig.,  Spinal  tract  of  trigeminal  nerve.  C.  r., 
Corpus  restiforme.  N.  ii.  c.  d..  Dorsal  nucleus  of  cochlear  nerve.  D.  r.  YIII, 
Descending  root  of  vestibular  nerve.  A^.  d.  r.  Till,  Nucleus  of  descending 
root  of  vestibular  nerve.     St.  (ic,  Acoustic  striae. 


46  THE    AXATOIMY    OF    THE    BKAIN. 

the  hypoglossal  nerve,  the  ala  cinerea  containing  the  terminal 
nuclei  of  the  ninth  and  tenth  cranial  nerves,  and  the  acoustic 
area.  In  this  situation  the  latter  contains  the  descending  root 
of  the  vestibular  nerve  and  its  accompanying  nucleus  medial 
to  it.  Lateral  and  ventral  to  this  is  seen  the  cross-section  of 
the  corpus  restiforme.  It  is  composed  of  fibres  from  several 
sources:  first,  the  direct  cerebellar  tract  from  the  cord,  which 
is  here  seen  entering  it;  second,  the  cerebello-olivary  fibres; 
and,  third,  the  external  arcuate  fibres.  The  cerebello-olivary 
fibres  connect  the  cerebellar  hemisphere  of  one  side  with  the 
olive  of  the  opposite  side.  They  run  in  the  corpus  restiforme, 
appear  among  the  most  ventral  of  the  internal  arcuate  fibres, 
traverse  the  olive  of  the  same  side,  cross  the  raphe,  and  enter 
the  olive  of  the  opposite  side.  The  external  arcuate  fibres 
consist  of  two  sets  (Fig.  21):  a  dorsal,  derived  from  the  nuclei 
of  the  funiculi  of  Goll  and  Burdach,  and  a  ventral,  which 
emerge  from  the  interolivary  layer  of  the  lemniscus  to  wind 
around  the  lateral  surface  of  the  medulla  and  enter  the  corpus 
restiforme. 

In  Eig.  22  the  section  passes  through  the  acoustic  strise. 
Laterally  these  fibres  are  connected  with  a  semilunar  mass  of 
gray  matter  dorso-lateral  to  the  corpus  restiforme:  the  acous- 
tic tubercle,  or  dorsal  nucleus  of  the  cochlear  nerve  (nucleus 
nervi  cochleae  dorsalis).  The  acoustic  nerve  at  the  medulla 
is  composed  of  two  parts:  a  postero-lateral,  or  cochlear, 'por- 
tion (radix  cochlearis);  and  an  antero-medial,  or  vestibidar, 
portion  (radix  vestibularis).  Xow,  the  acoustic  tubercle  is 
one  of  the  terminal  nuclei  of  the  cochlear  portion.  The  axones 
from  the  cells  of  this  nucleus  form  the  acoustic  striae,  which 
arch  in  the  floor  of  the  ventricle  first  dorsalward  and  then 
ventral  ward  toward  the  median  line;  just  ventral  to  the 
median  sulcus  most  of  them  cross  the  median  line,  and  their 
subsequent  course  will  be  described  hereafter. 

The  nuclei  of  the  twelfth,  tenth,  and  ninth  cranial  nerves 
have  ceased  to  exist  at  this  level  of  the  medulla,  while  the, 
descending  root  of  the  vestibular  nerve  is  larger  in  volume. 

The  medial  longitudinal  bundle  here  begins  to  show  as 
a  distinct  tract;  it  will  be  noticed  that  its  fibres  are  larger 
than  those  of  the  medial  lemniscus. 


THE    INTERXAL    AXATOMY    OF    THE    EXCEPHALOX. 


47 


Fig.  23. — A.,  p.  c,  Anterior  peduncle  of  cerebellum.  C.  f.  r.,  Fibres  from 
vestibular  nerve  to  cerebellum.  N.  B.,  Nucleus  of  Bechterew.  Is.  D.,  Xucleus 
of  Deiters.  C.  v.,  Corpus  restiforme.  T'.  Till,  Root-fibres  of  vestibular  nerve. 
N.  V.  n.  c,  A^entral  nucleus  of  cochlear  nen-e.  C.  Till,  Cochlear  portion  of 
acoustic  nerve.  Till,  Acoustic  nerve.  C.  trap..  Trapezoid  body.  Tr.  sp. 
n.  tri(j.,  Spinal  tract  of  trigeminal  nerve.  N.  o.  inf.,  Inferior  olivary  nucleus. 
Pyr.,  Pyramid.  Med.  lem..  Medial  lemniscus.  ^((C'.  T7/,  Xucleiis  of  facial 
nerve.  M.  I.  1).,  Medial  longitudinal  bundle.  Suhs.  gel..  Substantia  gelatinosa. 
M.  11.  v..  Medial  nucleus  of  vestibular  nerve. 


48  THE   AXATOMT    OF    THE    BKAIN. 

THE    IXTEEXAL    AZS'ATOMY    OF    THE    METEXCEPHALOX. 

The  Pox^s  Yajrolii. — We  sliall  begin  tlie  stndj  of  tlie 
pons  by  examining  a  section  throngli  the  transition-plane  be- 
tween tbe  medulla  and  j)ons  (Fig.  23).  Here  we  find,  as  in 
preceding  sections,  the  pyramid,  the  olive,  the  internal  arcuate 
fibres  and  medial  lemniscus,  the  medial  longitudinal  bundle, 
and  the  spinal  tract  of  the  trigeminal  nerve;  but  the  pre- 
dominant feature  of  the  section  is  presented  by  the  nuclei  of 
the  eighth  cranial  or  acoustic  nerve.  The  acoustic  tubercle 
is  no  longer  seen,  biit  ventro-lateral  to  the  corpus  restif orme, 
which  is  now  entering  the  cerebellum,  is  the  principal  nucleus 
of  termination  of  the  cochlear  nerve,  the  A'entral  nucleus 
(nucleus  nervi  cochleae  ventralis),  characterized  by  the  large 
number  of  nerve-fibres  contained  in  it  and  by  their  "basket- 
work-like"  arrangement  around  gToups  of  cells.  The  acoustic 
nerve  consists  of  two  distinct  bundles:  the  one  arises  from 
the  ganglion  of  Corti  in  the  cochlea,  and  is  therefore  called 
the  cochlear  nerve  (nervus  cochleae) ;  while  the  other  springs 
from  the  ganglion  of  Scarpa  in  the  vestibule,  and  is  termed 
the  vestibular  nerve  (nervus  vestibuli).  As  the  acoustic  nerve 
approaches  its  termination,  the  cochlear  nerve  enters  the  ven- 
tral nucleus,  where  it  bifurcates,  sending  a  part  of  its  fibres 
into  the  dorsal  nucleus,  the  others  ending  in  the  ventral 
nucleus.  A  series  of  sections  shows  that  the  dorsal  nucleus 
is  continuous  with  the  ventral  nucleus,  although  it  does  not 
extend  as  far  forward  as  the  latter.  In  the  dorsal  nucleus  the 
acoustic  striae  take  their  origin;  the  ventral  nucleus  sends  its 
axones,  seen  better  in  the  next  section,  nearly  transversely  into 
the  pons,  where  they  form  the  trapezoid  body  (corpus  trape- 
zoideum). 

The  fibres  of  the  vestibular  nerve  enter  the  pons  and  run 
toward  the  flood  of  the  ventricle ;  near  it,  in  the  area  acustica, 
they  reach  their  principal  nucleus  of  termination,  the  medial 
(nucleus  nervi  vestibuli  medialis) :  a  large  gray  mass  extend- 
ing in  the  floor  of  the  ventricle  from  its  lateral  wall  almost 
to  the  median  line.  Here  the  vestibular  fibres  divide  into 
their  ascending  and  descending  branches.  Most  of  the  former 
terminate  in  the  medial  nucleus,  but  some  turn  laterally  to 


THE    INTERNAL    ANATOilY    OF    THE    EXCEPHALON, 


49 


A,  p. 


TnspY 


Fig.  24. — M.  n.  v.,  Medial  nucleus  of  vestibular  nerve.  Niic.  YI,  Nucleus 
of  abducens  nerve.  G.  Til,  Genu  of  facial  nerve.  M.  J.  h..  INIedial  longi- 
tudinal bundle.  P.  p.  VII,  Pars  prima  of  facial  nerve.  YI,  Root-fibres  of 
abducens  nerve.  0.  a.,  Anterior  oliAje.  Med.  Jem.,  Medial  lemniscus.  D.  t.  f., 
Deep  transverse  fibres  of  pons.  Pyr.,  Pyramidal  tract.  S.  t.  f.,  Superficial 
transverse  fibres  of  pons.  N.  p.,  Nuclei  pontis.  Nvc.  YII,  Nucleus  of  facial 
nerve.  C.  tf-ap.,  Trapezoid  body.  P.  s.  YII,  Pars  secunda  of  facial  nerve. 
Tr.  sp.  Y.,  Spinal  tract  of  trigeminal  nerve.  A.  p.  c,  Anterior  peduncle  of 
cerebellum. 


50  THE    AXATOMY    OP    THE    BEAIIT. 

disappear  iu  the  superior  nucleus  of  Becliterew  and  in  tlie 
cerebellum.  The  descending  branches  form  the  descending 
root  of  the  vestibular  nerve,  which  we  have  seen  extending  as 
far  as  the  termination  of  the  funiculus  of  Burdach  accompanied 
bj  its  terminal  nucleus,  which  lies  medial  to  it  and  which  is  a 
prolongation  from  the  medial  nucleus. 

As  the  vestibular  fibres  approach  the  floor  of  the  ven- 
tricle they  traverse  a  scattered  collection  of  large  cells  medial 
to  the  dorsum  of  the  corpus  restiforme  known  as  the  nucleus 
of  Deiters  (nucleus  nervi  vestibuli  lateralis);  similarly  the 
cerebellar  fibres  of  this  nerve  pass  through  another  nucleus 
dorso-lateral  to  that  of  Deiters:  the  nucleus  of  Bechterew 
(nucleus  nervi  vestibuli  superior). 

Another  new  feature  of  this  section  is  the  nucleus  of 
origin  of  the  seventh  cranial,  or  facial,  nerve.  It  may  be 
looked  upon  as  a  forward  continuation  of  the  nucleus  ambiguus, 
and  occupies  the  same  relative  position  as  that  nucleus. 

The  next  section  (Fig.  24)  is  entirely  within  the  pons. 
Sections  of  the  pons  are  divided  into  two  parts:  dorsal  (pars 
dorsalis);    and  ventral,  or  basilar  (pars  basilaris). 

In  the  ventral  portion  we  find  two  sets  of  fibres:  longi- 
tudinal and  transverse.  The  former  are,  in  the  main,  the  fibres 
which  in  the  medulla  constitute  the  pyramids,  and  which  may 
be  still  called  the  pyramidal  tracts;  they  are  broken  up  into 
several  bundles  (fasciculi  longitudinales)  in  the  pons  by  trans- 
verse fibres. 

The  transverse  fibres  are  divided  into  two  sets  according 
to  their  relation  to  the  longitudinal:  those  which  run  ventral 
to  the  pyramidal  tracts  (fibrse  transversse  superficiales),  and 
those  dorsal  to  the  pyramidal  tracts  (fibrse  transversse  pro- 
fundse). 

Interspersed  among  these  transverse  fibres  are  several 
masses  of  gray  matter:,  the  nuclei  of  the  pons  (nuclei  pontis). 

Some  of  the  transverse  fibres  pass  entirely  across  the  sec- 
tion, being  fibres  which  connect  the  two  hemispheres-  of  the 
cerebellum;  others  come  from  the  cerebellum  and  end  in  the 
nuclei  pontis;  and  still  others  run  from  the  nuclei  pontis  to 
the  cerebellum. 

The  ventral  portion  of  the  pons  maintains  "essentially  the 


THE    IXTEEXAL    AXATOMY    OF    THE    EXCEPHALOX.  51 


CM— 


-IT 


Fig.  25.— Scheme  of  the  nuclei  and  root-fibres  of  the  cranial  nen'es 
(after  Edinger). 


52  THE    AXATOMT    OF   THE    BEAIX. 

same  appearance  tlirougliout  the  pons,  and  need  not  be  de- 
scribed again. 

Turning  now  to  tlie  dorsal  portion  of  the  pons,  it  is  seen 
that  the  medial  lemniscus  occupies  the  same  position  as  in 
previous  sections,  but  is  somewhat  flattened.  The  inferior 
olivary  nucleus  has  disappeared,  and  the  medial  lemniscus  is 
now  clearly  separated  from  the  medial  longitudinal  bundle. 
Lateral  to  the  medial  lemniscus  is  a  folded  sheet  of  gray  mat- 
ter: the  anterior  (superior)  ohve  (nucleus  olivaris  superior). 
Running  transversely  ventral  to  this  are  the  fibres  of  the 
trapezoid  body,  which,  as  we  have  seen,  are,  in  the  main,  the 
axones  of  cells  of  the  ventral  cochlear  nucleus.  Some  of  them 
terminate  in  the  anterior  olive' of  the  same  side,  while  others 
cross  the  median  line  to  end  in  the  anterior  olive  of  the  op- 
posite side. 

Dorsal  and  lateral  to  the  olive  is  the  nucleus  of  origin 
of  the  facial  nerve.  In  this  section  the  root-fibres  of  this 
nerve  have  been  di^^ded  in  three  places,  owing  to  the  fact 
that  they  pursue  a  very  complex  course  in  the  substance  of 
the  pons  (Fig.  25).  After  their  origin  the  fibres  take  a  dorso- 
medial  direction  until  they  reach  the  floor  of  the  ventricle  near 
the  median  line  (pars  prima);  then  they  run  longitudinally 
forward  to  make  a  lateral  bend  and  curve  dorsal  to  the  nucleus 
of  the  sixth  cranial  or  abducens  ner.  e  (genu) ;  and  finally 
assume  a  ventro-lateral  direction  to  pass  between  their  own 
nucleus  and  the  gelatinous  substance  (pars  secunda),  and  make 
their  exit. 

In  the  hollow  of  the  genu  of  the  facial  is  the  nucleus  of 
origin  of  the  sixth  cranial,  or  abducens,  nerve.  Its  root-fibres 
run  ventralward,  with  an  inclination  backward,  to  escape  in 
the  transverse  sidcus  between  the  pons  and  the  medulla. 

Lateral  to  the  pars  secimda  of  the  facial  is  the  spinal  tract 
of  the  trigeminal  nerve,  Avith  its  terminal  nucleus;  and  in  the 
extreme  lateral  area  of  the  floor  of  the  ventricle  is  still  a  por- 
tion of  the  medial  vestibular  nucleus,  with  a  few  root-fibres 
entering  it. 

Bordering  the  ventricle  is  the  cross-section  of  the  anterior 
peduncle  of  the  cerebellum  (brachium  conjunctiATim). 

The  next  section  (Lig.  26)  passes  through  the  domain  of 


THE   I^STTEEXAL   AXATOilY    OF    THE    EXCEPHALOX. 


53 


VV- 


'„    'ill.^^ri A.n.C. 


Fig.  26. — F.  F.,  Anterior  medullary  velum.  A.  p.  c.  Anterior  peduncle 
of  cerebellum.  P.  m.  n.  v.,  Principal  motor  nucleus  of  the  trigeminal  nerve. 
X.  ^.  v.,  Sensory  nucleus  of  trigeminal  nerve.  M.  v.,  INIotor  root-fibres  of 
trigeminal  nerve.  »S'.  v.,  Sensory  root-fibres  of  trigeminal  nerve.  C.  trap., 
Trapezoid  body.  0.  a.,  Anterior  olire.  Pyr.,  Pyramidal  tract.  S.  t.  f.,  Super- 
ficial transverse  fibres  of  the  pons.  D.  t.  f.,  Deep  transverse  fibres  of  the 
pons.  i\'.  p.,  Nuclei  pontis.  Med.  lem.,  Medial  lemniscus.  M.  I.  &.,  Medial 
longitudinal  bundle.     A.  f.  v.,  Arcuate  fibres  of  the  trigeminal  nerve. 


54  THE    ANATOMY    OF    THE    BEAIX. 

tlie  nuclei  of  tlie  trigeminal  nerve.  As  that  nerve  appears  at 
the  ventral  surface  of  the  pons  it  presents  two  divisions  or 
roots,  the  larger,  or  sensory,  portion  (portio  major)  being 
posterior  and  lateral  to  the  smaller,  or  motor,  root  (portio 
minor).  The  terminal  nucleus  of  the  sensory  portion  is  situ- 
ated deep  in  the  lateral  area  of  the  pons;  here  the  fibres  divide 
into  ascending  and  descending  branches;  the  latter  accom- 
panied by  their  nucleus  of  termination  we  have  seen  in  all 
the  preceding  sections  as  the  spinal  tract  of  the  trigeminal 
nerve.  Most  of  the  ascending  branches  terminate  in  the  large 
nucleus  seen  in  this  section,  which  may  be  regarded  as  the 
anterior  extremity  of  the  substantia  gelatinosa,  but  some  turn 
laterally  to  enter  the  middle  peduncle  of  the  cerebellum. 

The  anterior,  or  motor,  root  of  the  trigeminal  nerve  has 
two  nuclei  of  origin,  the  principal  one  of  which  is  seen  in  this 
section  (nucleus  motorius  princeps  nervi  trigemini)  as  a  small 
mass  of  large  cells  medial  to  the  sensory  nucleus.  Between 
these  two  nuclei  a  band  of  fibres  iims  toward  the  floor  of  the 
ventricle,  then  turns  medial  ward,  and,  passing  just  beneath 
the  floor  of  the  ventricle,  decussates  with  a  similar  tract  from 
the  other  side.  These  fibres  are  often  called  the  arcuate  fibres 
of  the  trigeminal,  but  neither  their  origin  nor  their  termina- 
tion has  been  definitely  determined. 

Between  the  medial  longitudinal  bundle  and  the  medial 
lemniscus  is  quite  a  large  collection  of  gray  matter  in  the 
raphe  and  on  each  side  called  the  central  nucleus  of  the  pons 
(shown  in  Mg.  2Y). 

It  will  be  noticed  that  the  anterior  olive  is  placed  farther 
lateral  than  in  the  preceding  section. 

The  last  section  of  the  pons  that  we  shall  examine  (Fig. 
27)  is  through  the  extreme  anterior  part  of  the  fourth  ven- 
tricle. In  the  anterior  medullary  velum  covering  the  ven- 
tricle is  the  decussation  of  the  fourth  cranial,  or  trochlear, 
nerve.  The  trochlear  nerve  springs  from  a  nucleus  in  the 
floor  of  the  aqueduct  of  Sylvius  farther  forward  at  the  level 
of  the  posterior  (inferior)  coUiculi;  it  then  runs  in  a  dorsal 
and  posterior  direction  to  gain  the  anterior  medullary  velum, 
in  which  it  entirely  crosses  to  the  opposite  side. 

Lateral  to  the  ventricle  is  a  small  bundle  of  fibres  semi- 


THE    INTEEXAL    AXAT0:MY    OF    THE    EXCEPHALOX, 


55 


D.i:-W])fdny. 


L-oc.coer: 


Cen  nuc^ 

Me  diem. -^ 


Fig.  27. — lY,  Trochlear  nerve.  Aq.  S.,  Aqueduct  of  Sylvius.  D.  r.  V., 
Descending  root  of  the  trigeminal  nerve.  N.  d.  r.  v.,  Nucleus  of  descending 
root  of  trigeminal  nerve.  A.  p.  c,  Anterior  peduncle  of  the  cerebellum. 
Lat.  lem.,  Lateral  lemniscus.  Nuc.  hit.  lem.,  Nucleus  of  lateral  lemniscus. 
Med.  lem.,  Medial  lemniscus.  Cen.  nvc,  Central  nucleus  of  pons.  Loc.  ccer., 
Locus  coeruleus.     Pyr.,  Eegion  of  pyramidal  tract.     N.  i).,  Nuclei  pontis. 


56  THE    ANATOMY    OF    THE    BEAIN. 

lunar  on  cross-section;  tliis  is  tlie  descending  root  of  tie  tri- 
geminal nerve  (radix  descendens  nervi  trigemini).  It  arises 
from  cells  in  the  neighborhood  of  the  locus  cceruleus,  which 
lies  medial  and  ventral  to  it.  These  cells  constitute  the  minor 
motor  nuclei  of  the  trigeminal  nerve  (nuclei  motorii  minores 
nervi  trigemini).  The  descending  root  can  be  traced  in  the 
lateral  wall  of  the  aqueduct  of  Sylvius  as  far  forward  as  the. 
level  of  the  anterior  (superior)  colliculi.  Its  fibres  descend 
to  join  those  springing  from  the  principal  motor  nucleus. 

Yentral  to  the  ventricle  on  each  side  of  the  median  line 
is  the  medial  longitudinal  bundle,  prominent  on  section  as  a 
triangular  tract  of  large  fibres. 

The  medial  lemniscus  is  now  so  flattened  that  its  trans- 
verse diameter  exceeds  the  vertical;  moreover,  it  has  retired 
from  the  raphe,  and  joined  neai-ly  at  right  angles  another 
tract:  the  lateral  lemniscus  (lemniscus  lateralis).  At  the 
angle  of  junction  is  situated  a  small  mass  of  gray  matter :  the 
nucleus  of  the  lateral  lemniscus  (nucleus  lemnisci  lateralis). 
A  series  of  sections  through  this  region  shows  that  the  nucleus 
of  the  lateral  lemniscus  is  continuous  with  the  anterior  ex- 
tremity of  the  anterior  olive.  iSTow,  we  have  seen  that  the 
fibres  of  the  trapezoid  body,  derived  in  part  from  the  ventral 
nucleus  of  the  cochlear  nerve,  terminate  in  the  anterior  olive 
of  both  sides.  From  each  olive  and  nucleus  of  the  lateral 
lemniscus  arises  another  set  of  fibres,  which  together  with 
the  striae  acusticas,  probably,  of  the  other  side  compose  the 
lateral  lemniscus.  Consequently  the  lateral  lemniscus  is  re- 
garded as  the  path  toward  the  cerebrum  of  impulses  brought 
to  the  pons  by  the  cochlear  nerve:  i.e.,  as  a  part  of  the  audi- 
tory conduction-path. 

In  the  ventral  portion  of  the  section  it  will  be  noticed 
that  the  aggregate  area  of  the  longitudinal  fibres  is  greater 
than  in  the  preceding  sections  of  the  pons;  this  is  due  to  the 
fact  that  many  of  the  longitudinal  fibres  are  distributed,  to 
the  motor  nuclei  of  cranial  nerves  and  to  the  nuclei  pontis  in 
the  anterior  portion  of  the  pons.  Since  the  fibres  distributed 
to  the  nuclei  pontis  arise  in  the  cortex  of  the  telencephalon, 
they  are  called  cortico-pontile  fibres. 


THE    INTERNAL   ANATOMY    OF    THE    ENCEPHALON.  57 


Nucleuse/entfilhs. 


Fig.  28.— Longitudinal  section  of  the  hemisphere  of  the  cerebellum 
(after  Gray). 


58  THE  ANATOMY  OF  THE  BEAIN.  , 

THE  INTERNAL  ANATOMY  OF  THE  CEREBELLUM. 

An  antero-posterior  median  section  tlirougli  the  worm 
of  the  cerebellum  shows  the  characteristic  arrangement  of 
its  white  and  gray  matters  (Fig.  8).  The  white  matter  is 
internal,  and  consists  of  a  central  mass,  or  trunk,  from  which 
prolongations  or  limbs  proceed  in  various  directions,  the  whole 
constituting  the  arbor  vitse.  The  primary  branches  emit  still 
smaller  secondary  branches,  which  are  invested  by  the  super- 
ficial gray  matter,  or  cortex  (substantia  corticalis).  The  depth 
of  the  larger  sulci  separating  the  various  lobules  can  now  be 
appreciated.  The  white  matter  of  the  worm  is  continuous  on 
each  side  with  that  of  the  hemisphere,  and  in  front  with  the 
anterior  medullary  velum,  resting  on  the  dorsum  of  which  is 
a  small  lobule  of  the  worm  called  the  lingula. 

In  the  hemispheres  the  arrangement  of  the  two  matters 
(Fig.  28)  is  quite  similar  to  that  in  the  vermis.  The  trunk 
of  the  arbor,  however,  is  larger,  and  contains  a  folded  lamella 
of  gray  matter — named,  from  its  serrated  appearance,  the 
nucleus  dentatus — situated  just  lateral  to  the  worm.  A  much 
smaller  nucleus  is  found  in  the  ventral  extremity  of  the  ante- 
rior vermiform  process  on  each  side  of  the  middle  line:  the 
nucleus  fastigii.  Lateral  to  the  nucleus  fastigii  are  located 
two  other  nuclei:  the  nucleus  gioborus  and  the  nucleus  em- 
bolifomiis. 

In  addition  to  the  fibres  which  connect  the  two  hemi- 
spheres and  to  those  which  connect  different  parts  in  the  same 
division,  the  white  matter  of  the  cerebellum  consists  of  fibres 
which  bring  it  into  communication  with  other  portions  of  the 
central  nervous  system.  Although  much  study  has  been  de- 
voted to  the  termination  of  the  fibres  which  enter  the  cere- 
bellum as  well  as  to  the  destination  of  those  which  originate 
in  its  gray  matter,  our  knowledge  in  both  particulars  is  far 
from  exact;  so  that  at  the  present  time  only  a  provisional 
account  can  be  given  of  the  connections  of  the  cerebellum. 
These  connections  are  established  mainly  through  its  several 
peduncles.  We  begin  with  the  inferior  peduncle,  or  corpus 
restiforme.  This,  we  have  learned,  contains  three  .sets  of 
fibres:    the  direct  cerebellar  tract  from  the  cord;    the  cere- 


THE    IjSTTEENAL   AXATOMY    OF    THE    EXCEPHALOX.  59 

bello-olivary  fibres,  running  both  ways  between  the  inferior 
olivary  nucleus  of  one  side  and  the  hemisphere  of  the  cere- 
bellum of  the  other;  and  the  extei-nal  arcuate  fibres,  ventral 
and  dorsal.  Thus,  the  cerebellum  is  connected  by  the  direct 
cerebellar  tract  with  Clarke's  cells  (nucleus  dorsalis)  of  the 
cord,  by  the  cerebello-olivary  fibres  with  the  olive  of  the  op- 
posite side  of  the  medulla,  and  by  the  external  arcuate  fibres 
with  the  terminal  nuclei  of  the  dorsal  funiculi  of  the  cord  on 
the  same  and  on  the  opposite  side.  It  has  been  generally 
thought  that  the  direct  cerebellar  tract  terminates  in  the 
nucleus  fastigii  of  the  worm;  but  recent  investigations  ren- 
der it  probable  that  this  tract  ends,  in  part  at  least,  in  the 
cortex  of  the  hemisphere,  and  that,  indeed,  all  the  fibres  which 
enter  the  cerebellum  by  way  of  the  corpus  restiforme  may 
reach  the  cortex. 

The  middle  peduncle  of  the  cerebellum  (brachium  pontis) 
contains  two  sets  of  fibres:  the  ponto-cerebellar  fibres,  which 
arise  in  the  nuclei  pontis  and  terminate  chiefly  in  the  hem- 
isphere of  the  opposite  side;  and  the  cerebello-pontile  fibres, 
which  run  from  the  hemisphere  to  the  pons,  where  some  of 
them  terminate  in  the  nuclei  pontis  and  others  go  to  an  un- 
known destination. 

The  anterior,  or  superior,  peduncle  (brachium  conjunc- 
tivum)  is  composed  of  fibres  which  arise,  according  to  some 
authorities,  in  the  nucleus  dentatus ;  according  to  others,  partly 
in  the  cortex  of  the  hemisphere.  They  enter  the  mesenceph- 
alon, where  they  decussate,  and  terminate  in  a  gray  mass  there 
found,  called  the  red  nucleus  (nucleus  ruber). 

In  addition  to  these  the  cerebellum  has  two  other  con- 
necting tracts.  In  studying  the  sections  of  the  pons  and  me- 
dulla we  saw  that  the  vestibular  nerve  sends  a  fasciculus  into 
the  cerebellum;  the  trigeminal,  glosso-pharyngeal,  and  vagus 
nerves  possibly  do  the  same  thing.  In  the  case  of  the  vestib- 
ular nerve  the  bundle  has  been  traced  to  the  nucleus  fastigii 
of  the  worm.  Some  fibres,  .then,  of  the  sensory  cranial  nerves 
run  directly  into  the  cerebellum. 

The  second  is  the  tract  of  Gowers  from  the  cord.  Al- 
though this  tract  is  in  reality  very  complex,  a  large  proportion 
of  its  fibres  runs  forward  as  far  as  the  level  of  entrance  of 


60  THE    ANATOMY    OF    THE    BKAIN. 

the  sensory  portion  of  the  trigeminal  nerve.  The  fibres  then 
tnrn  dorsahvard,  and,  having  reached  the  level  of  the  ante- 
rior medullary  velum,  run  backward  medial  to  the  anterior 
]3edimcle  to  end  in  the  cortex  of  the  worm. 

Finally,  the  results  of  many  investigators  point  to  the 
existence  of  fibres  which,  originating  in  the  gray  matter  of 
the  cerebellum,  establish  connection  with  the  cells  of  the 
ventral  horns  of  the  cord.  Unfortunately,  our  knowledge 
concerning  them  is  quite  indefinite.  It  would  seem  that 
one  important  connection  is  established  by  way  of  Deiters's 
nucleus. 

THE    INTERIS^AL    ANATOMY    OF    THE    MESENCEPHALOX. 

We  begin  the  study  of  the  mesencephalon  by  examining 
a  transverse  section  through  the  posterior,  or  inferior,  coUiculi 
(Fig.  29);  the  ventral  portion  of  such  a  section,  however, 
passes  through  the  anterior  margin  of  the  pons.  The  fourth 
ventricle  has  now  given  place  to  the  aqueduct  of  Sylvius 
(aquseductus  cerebri):  a  narrow  canal  whose  walls  contain  a 
considerable  amount  of  gray  matter.  In  this  gray  matter 
ventro-lateral  to  the  aqueduct  lies  the  nucleus  of  origin  of 
the  fourth  cranial,  or  trochlear,  nerve  (nervus  trochlearis). 
Its  root-fibres  curve  dorsalward  with  an  inclination  tow^ard  the 
median  line,  then  take  a  posterior  direction  to  enter  the  ante- 
rior medullary  velum,  where  they  cross  the  median  line  and 
appear  as  the  nerve  lateral  to  the  peduncle  of  the  cerebrum. 

Lateral  to  the  root-fibres  of  this  nerve  is  still  seen  the 
descending  root  of  the  trigeminal  nerve,  with  its  nuclei,  and 
ventral  to  the  nucleus  of  the  fourth  nerve  is  the  prominent 
medial  longitudinal  bundle. 

The  formatio  reticularis  is  traversed  by  numerous  fibres 
froni  the  anterior  peduncle  of  the  cerebellum  (brachium  con- 
junctivum),  which  decussate  in  the  raphe  (decussatio  brachii 
conjunctivi),  and  take  a  forward  course  to  end  in  the  ■  red 
nucleus,  as  we  shall  presently  see.  It  will  be  noticed  that  the 
ventral  fibres  of  the  peduncle  are  the  first  to  decussate.  These 
ventral  fibres  are  in  reality  not  connected  with  the  cerebellum, 
but  form  a  commissure  between  the  superior  vestibular  .nuclei 
of  the  two  sides. 


THE    IXTEENAL    ANATOMY    OF    THE    EXCEPHALOX. 


Gi 


Post  col. 


NucW-     ■^'^^"'   ''' 


^-^-^    Zat.l 


M.lb. 


Cei2. 


nnc 


em. 


D.a.px, 
MedJem 


Fig.  29. — Fo8t.  col.,  Posterior  colliculus.  Aq.  S.,  Aqueduct  of  Sylvius. 
D.  r.  T.,  Descending  root  of  the  trigeminal  nerve  and  its  nucleus.  Lat.  lem., 
Lateral  lemniscus.  A.  p.  c,  Anterior  peduncle  of  cerebellum.  D.  a.  p.  c, 
Decussation  of  anterior  peduncle.  -  il/ed.  lem.,  Medial  lemniscus.  Cen.  nuc, 
Central  nucleus.  M.  I.  6.,  Medial  longitudinal  bundle.  ^X'nc.  IV,  Nucleus  of 
the  trochlear  nerve.  R.  IV,  Eoot-fibres  of  the  trochlear  nerve.  G.  p.  c.  Gray 
matter  of  posterior  colliculus. 


63  THE   AXATOMY    OF    THE    BKAIN. 

Ventral  to  tlie  peduncle  is  the  medial  lemniscns,  still  con- 
tinuous laterally  with  the  lateral  lemniscus.  The  latter  tract 
has  here  a  decided  dorsal  inclination,  and  terminates  by  aban- 
doning some  of  its  fibres  to  the  medial  geniculate  body  through 
the  posterior  brachium,  and  others  to  the  central  gray  matter, 
of  the  posterior  colliculus — the  nucleus  of  the  posterior  (in- 
ferior) colliculus  (nucleus  colliculi  inferioris).  Some  of  the 
cells  of  this  nucleus  send  their  axones  forward  to  the  anterior 
colliculus,  while  others  enter  the  lateral  lemniscus  and  pursue 
a  posterior  direction  in  that  tract. 

The  second  section  (Fig.  30)  is  through  the  anterior 
(superior)  colliculi,  and  is  entirely  confined  to  the  mesen- 
cephalon. 

We  have  seen  that  the  mesencephalon  may  be  divided 
superficially  into  the  corpora  quadrigemina  and  the  peduncles 
of  the  cerebrum.  In  sections  each  peduncle  is  divided  into  a 
dorsal  portion — the  tegmentum — and  a  ventral  portion:  the 
crusta,  or  base  of  the  peduncle  (basis  pedunculi).  The  ground 
for  this  division  is  the  substantia  nigra,  a  mass  of  heavily-pig- 
mented  cells,  which  appears,  to  the  unaided  eye,  as  a  black 
streak  across  the  section  of  the  peduncle.  The  tegmentum  is 
separated  from  the  corpora  quadrigemina  by  an  arbitrary  line 
drawn  through  the  aqueduct. 

Taking  up  these  parts  separately,  it  will  be  seen  that  the 
fibres  contained  in  the  base  of  the  peduncle  are  longitudinal 
in  direction;  they  are  derived  from  the  cortex  of  the  telen- 
cephalon, and  we  have  seen  most  of  them  before  as  the  pyram- 
idal tract  and  the  cortico-pontile  fibres.  In  the  tegmentum 
dorsal  to  the  substantia  nigra  is  situated  the  reddish'  mass  of 
gray  matter  to  which  we  have  referred  as  the  red'  nucleus 
(nucleus  ruber),  in  which  terminates  the  anterior  peduncle  of 
the  cerebellum  after  its  decussation.  Its  medial  margin  is 
marked  by  the  section  of  a  small  bundle  of  fibres, — the  fascic- 
ulus retroflexus, — which  connects  the  trigonum  habenulse  of 
the  diencephalon  with  the  ganglion  interpedunculare :  a  mass 
of  gray  matter  found  between  the  beginning  of  the  peduncles 
(not  shown  in  the  figure). 

Lateral  to  the  red  nucleus  and  dorsal  to  the  lateral  ex- 
tremity of  the  substantia  nigra  lies  the  lemniscus,  its  section 


THE    INTEKNAL    ANATOMY    OF    THE    EXCEPHALON.  63 


L 


em. 


Antcoi^'^-      ^''^"      Ac^S. 


NucM 
-MU 

-    Nucmh. 

Fas.  ret. 
RM 


BP. 


Fig.  30.— An^.  col..  Anterior  colliculus.  St.  g.,  Stratum  griseum. 
St.  son.,  Stratum  zonale.  Aq.  S.,  Aqueduct  of  Sylvius.  Nuc.  Ill,  Nucleus 
of  the  oculomotor  nerve.  M.  I.  ft.,  Medial  longitudinal  bundle.  Nuc.  rub., 
Red  nucleus.  Fas.  ret..  Fasciculus  retroflexus.  R.  Ill,  Root-fibres  of  the 
oculomotor  nerve.  Subs,  nig.,  Substantia  nigra.  B.  P.,  Base  of  peduncle. 
Lem.,  Lemniscus.     St.  al.  p.,  Deep  layer  of  white  matter. 


64  THE  anato:mt  of  the  beaix. 

being  somewliat  comma-sliaped,  with  its  small  extremity  point- 
ing dorsalward.  In  this  situation  the  bundle  gives  off  some 
fibres  to  the  anterior  eolliculus,  but  most  of  it  is  continued  on 
to  the  diencephalon. 

Yentral  to  the  aqueduct  on  each  side  of  the  median  line 
is  the  very  striking  nucleus  of  the  third  cranial,  or  oculomotor, 
nerve  (nervus  oculomotorius) ;  its  root-fibres  traverse  the  red 
nucleus  and  the  substantia  nigra,  to  emerge  at  the  medial  bor- 
der of  the  peduncle.  It  will  be  noticed  that  some  of  these 
fibres  arise  from  the  nucleus  of  the  opposite  side:  i.e.,  the 
nerve  undergoes  a  partial  decussation.  Immediately  ventral 
to  the  nucleus  of  the  third  nerve  is  the  section  of  the  medial 
longitudinal  bundle. 

The  anterior  colliculus  is  covered  by  a  thin  sheet  of  white 
matter, — the  stratum  zonale, — which  consists,  to  a  large  ex- 
tent, of  fibres  from  the  optic  tract  on  their  way  to  terminate 
in  the  central  gray  matter  of  the  colliculus  (stratum  griseum 
colliculi  superioris).  Limiting  this  gray  stratum  medially  is 
another  zone  of  white  matter, — the  deep  white  stratum 
(stratum  album  profundum), — which  is  composed  of  fibres 
that,  arising  from  the  cells  of  the  gray  stratum,  curve  around 
the  aqueduct  to  enter  the  tegmentum  and  decussate  in  the 
raphe  ventral  to  the  medial  longitudinal  bundle.  Many  of 
them  are  believed  to  enter  the  medial  longitudinal  bundle  and 
form  a  constituent  part  of  it.  The  medial  longitudinal  bundle, 
then,  consists,  in  part,  of  the  axones  of  cells  contained  in  the 
gray  matter  of  the  colliculi,  in  which,  as  we  have  seen,  ter- 
minate fibres  from  the  optic  tracts  and  from  the  lemnisci. 
Now,  the  medial  longitudinal  bimdle  in  its  course  through 
the  mesencephalon  and  the  pons  can  be  seen  giving  off  fibres 
to  the  nuclei  of  the  motor  cranial  nerves,  especially  those 
which  innervate  the  ocular  muscles.  It  is,  therefore,  not  im- 
probable that  this  bundle  is,  to  a  large  extent,  a  connecting 
tract  between  the  corpora  quadrigemina  and  the  nuclei  of 
motor  cranial  nerves,  thus  permitting  certain  reflex  acts  due 
to  visual  and  acoustic  impressions.  Another  source,  however, 
for  the  fibres  of  this  bundle  is  found  farther  forward  in  the 
mesencephalon  in  the  shape  of  a  small  nucleus  lateral  to  the 
aqueduct,  and  known  as  the  nucleus  of  the  medial  longitudinal 
bundle  (nucleus  fasciculi  longitudinalis  medialis). 


THE    INTERNAL   ANATOMY    OF    THE    ENCEPHALON. 


65 


Por 


Jnt. 


cor. 


Scp-peL  .. 
Col.for.^'    ~ 

1^^ 

H-nuchcaad'-.  . 

!       \ 

Ant  com.- 

";  -  -  \              'J^ 

T.nucl.caud.-  -  -l_  _    ,       'f^ 

Mas.int —          _^w- 
Thai.    '--~^-~~jM- 

St  term — L_^  Wf      /  /, 

Paly,  •.,      /     ~^W         /  Ji 

y^^^^^M- 

Ant  col  .. 
Post  col. 

"'■''^^ 

IV' 


.n.mclcaud. 

J.l.int.cap. 

ExLcap. 
Is/. 

■Mici.  lent 
-   Claus. 
-Plintcap. 

Thai. 
...  C.j.m. 
■  T.nucl.caud 
Timb 

-hipp. 

...Post,  con 


Fig.  31. — For.,  Fornix.  Sep.  ftel.,  Septum  pellucidum.  Gol.  for.,  Column 
of  fornix.  E.  nucl.  caud.,  Head  of  nucleus  caudatus.  Ant.  com.,  Anterior 
commissure.  T.  nucl.  caud.,  Tail  of  nucleus  caudatus.  Mas.  int.,  Massa  inter- 
media. Thai,  Thalamus.  St.  term..  Stria  terminalis.  Pule,  Pulvinar.  Ant. 
col.,  Anterior  colliculus.  Post,  col.  Posterior  colliculus.  IT,  Trochlear  nerve. 
Ant.  cor.,  Anterior  cornu  of  lateral  ventricle.  A.  I.  int.  cap.,  Anterior  limb 
of  internal  capsule.  Ext.  cap..  External  capsule.  Jsh,  Island  of  Reil.  Nucl. 
lent..  Nucleus  lentiformis.  Glaus.,  Claustrum.  P.  I.  int.  cap.,  Posterior  limb 
of  internal  capsule.  Hipp.,  Hippocampus.  Post,  cor..  Posterior  cornu  of 
lateral  ventricle.     (After  Landois.) 


66  THE    AXATOilT    OF    THE    BRAIN. 

In  addition  to  tlie  fibres  derived  from  the  medial  longi- 
tudinal bundle  numerous  fibres  enter  tbe  nuclei  of  the  third 
and  fourth  cranial  nerves;  some  of  them  are  possibly  fibres 
which  have  come  down  from  the  cortex  of  the  telencephalon 
in  the  pyramidal  tracts,  and  thus  make  connection  between 
the  cortex  and  the  nuclei  of  these  two  nerves. 

THE    IXTEEXAL    AXATOMT    OF    THE    DIEKCEPHALOISr. 

The  Thalamus. — The  dorsal  surface  of  the  thalamus  is 
white,  owing  to  the  presence  of  a  thin  stratum  of  fibres 
(stratum  zonale)  derived  mostly  from  the  optic  tract. 

The  medial  surface  is  gray,  and  continuous  with  the  gray 
matter  lining  the  third  ventricle  and,  through  the  massa  in- 
termedia, with  the  opposite  thalamus. 

The  lateral  surface  of  the  thalamus  is  fused  with  the 
telencephalon.  To  appreciate  this  it  is  necessary  to  examine 
a  horizontal  section  through  the  cerebram'  (Fig.  31).  Such 
a  section  discloses,  in  addition  to  the  thalamus,  two  gray 
bodies,  which,  together,  constitute  the  corpus  striatum  of  the 
telencephalon;  the  anterior  is  the  caudate  nucleus,  and  the 
one  lateral  to  the  thalamus  is  the  lentiform  nucleus  of  the 
coi*pus  striatum.  The. thalamus  and  the  corpus  striatum  are 
often  called  the  "basal  ganglia"  of  the  cerebrum.  The  lenti- 
form nucleus  is  separated  from  the  caudate  nucleus  and  from 
the  thalamus  by  an  elbow-shaped  layer  of  white  matter:  the 
internal  capsule,  consisting  of  two  limbs,  anterior  and  poste- 
rior. 

A  vertical  transverse  section  through  the  thalamus  (Fig. 
32)  shows  that  it  is  composed  of  three  nuclei  more  or  less 
indistinctly  separated  by  thin  lamellee  of  white  matter;  they 
are  distinguished  as  the  lateral,  medial,  and  anterior  nuclei 
of  the  thalamus  (nucleus  lateralis,  n.  medialis,  et  n.  anterior 
thalami).  Some  anatomists  make  another  nucleus  out  of  the 
ventral  part  of  the  lateral  nucleus,  and  speak  of  it  as.  the 
ventral  nucleus.  From  the  cells  in  this  latter  portion  of  the 
thalamus  arise  numerous  fibres,  which,  having  passed  through 
the  posterior  limb  of  the  internal  capsule,  finally  terminate 
in  the  cortex  of  the  telencephalon ;  they  represent,  as  we  shall 
see  hereafter,  the  indirect  continuation  of  the  medial  lemniscus. 


THE    INTERNAL    ANATOMY    OF    THE    ENCEPHALON. 


67 


Nucicaud  . 

fhsc  thcilma/n. 
JVucUi^t.thfd 

^ucl.  ven.thaf. 
Int.C&p.- 

nuclsub. 

Coljon 
Corp- mo  TV.  | 

Tu6-  cm. 
Op.c/i. 


Jzl^up. 
IsUndH. 

JViicl.  lent? 

...  Ant  Com. 
Op.b^ 

JVi/cL&mwg. 


TbrfwJoic. 


Fig.  32. — 'Sucl.  caud.,  Nucleus  caudatus.  Xucl.  ant.  thai.,  Anterior  nu- 
cleus of  thalamus.  Fasc.  thai,  mam.,  Fasciculus  thalamo-mamillari.s.  Niicl. 
lat.  thai..  Lateral  nucleus  of  thalamus.  Med.  St.,  Medullaiy  stria.  Nucl.  ven. 
thai.,  Ventral  nucleus  of  thalamus.  Xucl.  vied,  thai..  Medial  nucleus  of  thala- 
mus. Int.  cap..  Internal  capsule.  B.  P.  ent.  cap..  Base  of  peduncle  of  cerebrum 
entering  the  internal  capsule.  Nucl.  sub..  Nucleus  hypothalamicus.  B.  P., 
Base  of  the  peduncle  of  cerebrum.  Col.  for..  Column  of  fornix.  Corp.  mam., 
Corpus  mamillare.  Till),  cin..  Tuber  cinereum.  Op.  ch..  Optic  chiasm.  F.  I. 
sup.,  Fasciculus  longitudinalis  superior.  Island  R.,  Island  of  Reil.  Claus., 
Claustrum.  Nncl.  lent.,  Nucleus  fentiformis.  Ant.  com.,  Anterior  commissure. 
Op.  tr.,  Optic  tract.     Nucl.  amyg.,  Nucleus  amygdala?.     (After  Edinger.) 


68  THE   ANATOMY    OP    THE    BEAIX. 

Another  bundle  of  fibres,  wliieh  runs  through  the  ante- 
rior limb  of  the  internal  capsule,  connects  the  thalamus  with 
the  cortex  of  the  telencephalon;  about  these  not  much  is 
known,  but  it  is  held  bv  some  that  the  thalamus  is  connected 
with  every  region  of  the  cortex. 

The  basal  ganglia  are  connected  with  each  other  by  fibres 
which  run  ventral  to  these  bodies. 

The  Hypothalamus. — Our  knowledge  of  this  region  of 
the  diencephalon  is  so  imperfect  that  a  very  brief  account  will 
suffice  here.  The  lamina  terminalis  and  the  tuber  cinereum 
are  composed  of  gray  matter.  The  infundibulum  is  a  diver- 
ticulum from  the  floor  of  the  third  ventricle  to  the  hypophy- 
sis. The  latter  body  is  peculiar  in  that  its  two  lobes  are 
entirely  different  in  structure;  the  posterior  lobe  contains 
nervous  substance,  while  the  anterior,  being  derived  from  the 
vault  of  the  pharynx,  consists  of  epithelial,  tubules. 

The  corpora  mamillaria  are  gray  internally  (Fig.  32),  and 
the  gray  matter  in  each  is  divided  into  three  nuclei  (nuclei 
corporis  mamillaris).  Each  corpus  receives  the  column  of  the 
fornix,  as  will  be  described  hereafter,  and  is  connected  with 
the  anterior  nucleus  of  the  thalamus  by  a  bundle  of  fibres,  the 
fasciculus  thalamo-mamillaris  of  Yicq  d'Azyr. 

Behind,  the  hypothalamus  is  fused  with  the  peduncle  of 
the  cerebrum,  the  plane  of  fusion  being  commonly  called  the 
subthalamic  region.  A  section  through  this  (Fig.  33)  shows, 
lateral  td  the  red  nucleus,  a  gray  body  not  seen  hitherto:  the 
subthalamic  nucleus  (nucleus,  hypothalamicus).  The  white 
matter  dorsal  to  this  nucleus  consists  largely  of  the  fibres  of 
the  medial  lemniscus.  This  tract  terminates  to  a  large  extent 
in  the  ventral  nucleus  of  the  thalamus,  from  the  cells  of  which 
run  axones  that  continue  the  course  of  the  lemniscus  to  the 
cortex  of  the  telencephalon.  Here  we  can  also  see  the  base 
of  the  peduncle  continuous  with  the  internal  capsule. 

The  Metathalamus.^ — The  interior  of  the  geniculate 
bodies  is  formed  by  gray  matter  known  as  their  nuclei  (nuclei 
corporis  geniculati  lateralis;  n.  c.  g.  medialis).  The  fibres  of 
the  optic  tract  terminate  largely  in  the  gray  matter  of  the 
lateral  geniculate  body,  but  the  tract  also  sends  some  fibres 
into  the  pulvinar  of  the  thalamus,  the  anterior  collic'ulus,  and 


THE    IXTEEXAL   ANATOMY    OF    THE    EXCEPHALOX. 


69 


Corp.  c^ J. 
For: 

Medjn 

Nucl.  rned  thai 
Nuclm  I  b.  ..' 

J^ec/.  nucl 

y5uL  nig. 

3^. 


-.  Muclcaud, 
^    Nuclkhthdl 
--.  In  heap. 
.    Zslcinc/. 
\Mici.  ren.  thcij, 

-..     Mec/J<2m, 
--  -  Nuci.hypotn, 

Op.tn 

Ant  com. 
Tail  vuclc^ud 
Jftpp. 

^  Temporal  lohe. 


Fig.  33. — Corp.  ml..  Corpus  callosum.  For.,  Fornix.  Med.  St.,  Medullary- 
stria.  Niicl.  med.  thai.,  Medial  nucleus  of  thalamus.  Nucl.  m.  I.  h.,  Nucleus 
of  medial  longitudinal  bundle.  Red  nucl.,  Eed  nucleus  of  the  tegmentum. 
Svh.  nig.,  Substantia  nigra.  B.  P.,  Base  of  the  cerebral  peduncle.  Nucl. 
caud.,  iSTucleus  caudatus.  N^icl.  lat.  thai..  Lateral  nucleus  of  thalamus.  Int. 
cap..  Internal  capsule.  Island,  Island  of  Kiel.  Nucl.  ven.  thai..  Ventral 
nucleus  of  thalamus.  Med.  lem.,  Region  of  the  medial  lemniscus.  Nucl. 
hypoth.,  Nucleus  hypothalamicus.  Op.  tr.,  Optic  tract.  Ant.  com..  Anterior 
commissure.  Tail  niicl.  caud..  Tail  of  nucleus  caudatus.  Hipp.,  Hippocam- 
pus.    (After  Edinger.) 


70  THE    AXATOMY    OF    THE    BRAIX. 

possibly  into  the  medial  geniculate  body.  Tlie  latter  body 
receives  most  of  the  lateral  lemniscus.  From  the  gray  matter 
of  the  lateral  geniculate  body,  the  pulrinar,  and  the  anterior 
colhculus  spring  fibres  which  run  through  the  posterior  limb 
of  the  internal  capsule,  continuing  the  course  of  the  optic 
tract  to  the  cortex  and  forming  the  so-called  occipito-thalamic 
radiation  of  Gratiolet;  while  those  from  the  medial  genicu- 
late body  continue  the  course  of  the  lateral  lemniscus  to  the 
cortex,  terminating  in  the  superior  temporal  convolution. 

THE    IXTEEXAL    AXAT0:\[Y    OF    THE    TELEXCEPHALOX. 

If  a  horizontal  section  be  made  through  the  hemispheres 
just  dorsal  to  the  level  of  the  corpus  callosum  (Fig.  34),  there 
is  brought  to  light  in  each  hemisphere  the  appearance  known 
as  the  centrum  semiovale,  or  central  mass  .of  white  matter, 
dotted  in  the  fresh  specimen  by  sections  of  blood-vessels :  the 
puncta  vasculosa.  The  centrum  is  bordered  by  a  thin  con- 
voluted margin  of  gray  matter:  the  cortex,  or  cortical  sub- 
stance (substantia  corticalis).  .  It  can  now  be  seen  that  each 
convolution  consists  of  a  central  mound  of  white  matter  cov- 
ered by  cortical  substance.  Moreover,  the  cortical  substance 
lines  even  the  deepest  sulci,  in  the  bottom  and  on  the  sides 
of  which  numerous  small  secondary  convolutions  are  seen. 
The  two  centra  semiovalia  are  connected  by  the  broad  band 
of  white  matter  pre\'iously  mentioned  as  the  corpus  callosum. 

The  Corpus  Oallosu:m. — rThis  body  should  be  studied 
in  sagittal  (Fig.  38),  as  well  as  in  horizontal,  sections  of  the, 
encephalon.  It  consists  of  a  central  portion,  or  trunk  (trun- 
cus),  and  two  extremities,  anterior  and  posterior.  The  dorsal 
surface  of  the  trunk  presents  on  each  side  of  the  median  line 
a  slender  longitudinal  band,  the  nerve  of  Lancisi,  or  medial 
longitudinal  stria  (stria  longitudinalis  medialis) ;  and  laterally 
at  the  junction  with  the  centrum  a  similar  band,  the  lateral 
longitudinal  stHa  (stria  longitudinalis  lateralis).  Between  the 
two  strife  stretches  an  exceedingly  delicate  gray  lamella:  the 
fasciola  cinerea. 

The  ventral  surface  of  the  trunk  is  concave,  and  forms 
the  roof  for  a  cavity  in  each  hemisphere:   the  lateral  ventricle. 


THE    INTERNAL   ANATOMY    OF    THE    ENCEPHALON. 


71 


Fig.  34. — G.,  Genu  of  corpus  callosum.  >S'/)Z.,  Splenium  of  corpus  eallosum. 
St.  I.  I.,  Lateral  longitudinal  stria.  St.  I.  m.,  Medial  longitudinal  stria.  F.  c, 
Pasciola  cinerea.    C,  Cortex.    Gen.  sem.,  Centrum  semiovale.     (After  Eauber.) 


72  THE   ANATOMY    OF   THE    BEAIN. 

The  posterior  extremity  is  thickened,  and  is  called  the 
splenium. 

The  anterior  extremity  is  the  knee  (genu);  here  the 
corpus  callosum  makes  a  ventral  bend,  which  is  continued 
backward  under  the  name  of  rostrum.  The  longitudinal  striae 
accompany  it  in  this  course,  and  under  the  name  of  peduncle 
of  the  corpus  callosum,  or  gyrus  subcallosus,  pass  to  the  ante- 
rior extremity  of  the  hippocampal  convolution,  as  previously 
described. 

The  great  bulk  of  the  fibres  of  the  corpus  callosum  are 
transverse  in  direction :  they  radiate  into  the  centra  semiovalia 
in  all  directions,  going  to  almost  all  parts  of  the  cortex.  They 
belong  to  the  class  of  commissural  fibres:  i.e.,  they  connect 
corresponding  parts  of  the  two  hemispheres. 

The  Lateral  Ventricles. — The  lateral  ventricle  (ven- 
triculus  lateralis)  of  each  hemisphere  may  be,  exposed  by  carry- 
ing an  antero-posterior  incision  through  the  corpus  callosum 
on  each  side  of  the  median  line,  and  severing  the  attachments 
of  that  body  in  front,  behind,  and  laterally.  It  is  a  wide  and 
shallow  cavity  divided  into  a  central  portion  (pars  centralis) 
and  three  prolongations,  or  horns  (cornua). 

The  anterior  horn  (cornu  anterius)  is  directed  forward 
and  lateralward  into  the  substance  of  the  frontal  lobe. 

The  posterior  horn  (cornu  posterius)  runs  backward, 
lateralward,  and  then  medialward  into  the  substance  of  the 
occipital  lobe;  it  is  marked  by  a  ridge  thrown  up  by  the  cal- 
carine  fissure:    the  calcar  avis. 

The  middle,  or  inferior,  horn  (cornu  inferius)  curves 
posterior  and  ventral  to  the  thalamus,  winding  backward, 
lateralward,  ventralward,  forward,  and  medialward  into  the 
temporal  lobe  nearly  to  its  anterior  extremity.  In  its  floor  is 
a  ridge,  produced  by  the  dentate  fissure,  following  the  course 
of  the  horn  throughout  its  length,  and  called  Ammon's  horn, 
or  the  hippocampiis.  / 

Keturning  to  the  central  portion  of  the  ventricle,  its  roof 
is  formed  by  the  corpus  callosum.  Its  lateral  wall  is  formed 
by  the  junction  of  the  corpus  callosum  with  the  white  matter 
of  the  hemisphere.  In  its  floor  are  seen  the  following  objects, 
starting  at  the  lateral  wall  and  proceeding  toward  the  median 


THE    INTEKNAL   AISTATOIIT    OF    THE    EXCEPHALOX. 


73 


Corpc&l 


Ant.com, 


[nFFr.  coni^ 


IslR. 

■  Fi'ssyl 
...   0}}c)C.^reQ, 
I.   Cl&us. 


Fig.  35. — Corip.  ml.,  Corpus  callosum.  Atit.  com.,  Anterior  commissure. 
Inf.  Fr.  conv.,  Inferior  frontal  convolution.  Ext.  cap.,  External  capsule. 
Isl.  R.,  Island  of  Reil.  Fis.  syl.,  Fissure  of  Sylvius.  Olfac.  area,  Olfactory- 
area.  Clans.,  Claustrum.  C.  n.,  Caudate  nucleus.  Int.  cap.,  Internal  capsule. 
Gl.  p.,  Globus  pallidus.     P.,  Putamen.     (After  Edinger.) 


74  THE    AXATOMY    OF    THE    BEAIN. 

line :  A  large  gourd-shaped  mass  of  gray  matter, — the  caudate 
nucleus  of  the  corpus  striatum;  then  the  stria  terminalis  and 
vena  terminalis;  then  the  lateral  half  of  the  dorsal  surface 
of  the  thalamus;  next  a  fringe  of  blood-vessels  rolled  in  pia 
mater;  the  chorioid  plexus  (plexus  chorioideus)  of  the  lateral 
ventricle ;  and,  finally,  one-half  of  a  triangular  sheet  of  white 
matter,  the  fornix,  which  has  a  half  in  each  lateral  ventricle. 
We  shall  now  study  each  of  these  objects  separately. 

The  Corpus  Striatum. — To  obtain  a  satisfactory  concep- 
tion of  the  corpus  striatum  and  the  neighboring  parts  of  the 
hemisphere  it  is  necessary  to  examine  a  series  of  transverse 
and  horizontal  sections  of  this  region  (Figs.  31,  32,  33,  35, 
and  36),  from  which  we  learn  the  following  facts:  The  corpus 
striatum  contains  two  distinct  collections  of  gray  matter,  one 
of  which  is  seen  in  the  floor  of  the  ventricle,  while  the  other 
is  imbedded  in  the  white  matter  lateral  to  the  ventricle.  The 
intraventricular  portion  is  the  caudate  nucleus  (nucleus  cau- 
datus);  it  begins  with  an  enlarged  anterior  extremity, — the 
head  (caput), — and  rapidly  tapers  backward  to  a  long,  narrow 
column:  the  tail  (cauda).  The  tail  first  arches  backward,  run- 
ning dorsal  and  then  lateral  to  the  thalamus;  it  then  turns 
forward  ventral  and  lateral  to  the  thalamus,  and  can  be  traced 
in  transverse  sections  along  the  roof  of  the  inferior  horn  of 
the  ventricle  to  a  thickened  portion  of  the  cortex  in  the  ante- 
rior extremity  of  the  temporal  lobe:  the  amygdaloid,  or 
almond-shaped,  nucleus  (nucleus  amygdalae). 

The  extraventricular  part  of  the  corpus  striatum  is  called 
from  its  shape  the  lentiform  nucleus  (nucleus  lentiformis). 
It  lies  in  a  plane  lateral  and  posterior  to  the  caudate  nucleus, 
from  which  it  is  separated  by  a  narrow  sheet  of  white  matter: 
the  anterior  limb  of  the  internal  capsule.  On  its  medial  side 
is  the  thalamus,  which,  however,  extends  farther  backward 
than  the  lentiform  nucleus;  from  this  it  is  separated  by  the 
posterior  limb  of  the  internal  capsule.  In  transverse  sections 
it  is  seen  that  the  lentiform  nucleus  is  composed  of  three 
divisions  separated  from  each  other  by  thin  planes  of  white 
matter;  the  lateral  and  highest  of  these  divisions  is  called  the 
putamen,  while  the  other  two  constitute  the  globus  pallidus. 
Lateral  to  the  nucleus  lentiformis  is  a  sheet  of  white  matter 


THE    INTERNAL    AKATOMY    OF    THE    EXCEPHALOX. 


Corp.  cal 
f^uclcdud- 
Chfh 

/\fuchnl:thi 
J^uclmedHidl 

Colfon 

Jnt.CaP- 

Gl.p&I- 

Ant.  ^" 


Genu  int.Cctp' 


Antr.com- 
rasc.uncin. 

Olf-ac  &rea. 


Fig.  36. — Corp.  cal.,  Corpus  callosum.  Nticl.  caiul.,  Nucleus  caudatus. 
Ch.  pi,  Chorioid  plexus.  NticJ.  ant.  thai.,  Anterior  nucleus  of  thalamus. 
Nucl.  med.  thai,  Medial  nucleus  of  thalamus.  Col  for.,  Column  of  the 
fornix.  Int.  cap.,  Internal  capsule.  Gl  jxil,  Globus  pallidus.  A7it.  com., 
Anterior  commissure.  Olf.  tr.,  Olfactory  tract.  Fasc.  long,  sup.,  Superior 
longitudinal  bundle.  Genu  int.  cap.,  Genu  of  internal  capsule.  Isl,  Island 
of  Eeil.  Clam.,  Claustrum.  Pvt.,  Putamen.  Fasc.  ttncin.,  Fasciculus  un- 
cinatus.     Olfac.  area.  Olfactory  ai=ea.     (After  Edinger.) 


76  THE   AXATOMY    OF    THE    BEAIN. 

known  as  tlie  external  capsule,  and  bordering  this  laterally  is 
a  thin  layer  of  gray  matter,  the  claustrum,  which  is  continuous 
ventrally  with  the  amygdaloid  nucleus;  still  farther  lateral 
we  recognize  the  convolutions  of  the  island  of  Eeil. 

The  Internal  Capsule. — The  internal  capsule  (capsula 
interna)  is  the  plane  of  white  matter  situated  between  the 
head  of  the  caudate  nucleus  and  the  thalamus  as  the  medial 
boundary,  and  the  lentiform  nucleus  as  the  lateral  boundary. 
It  may  be  divided  into  two  limbs,  or  portions:  an  anterior 
(pars  frontalis)  and  a  posterior  (pars  occipitalis).  The  former 
is  contained  between  the  head  of  the  caudate  nucleus  and  the 
lentiform  nucleus,  the  latter  between  the  lentiform  nucleus 
and  the  thalamus.  The  two  limbs  meet  at  an  obtuse  angle, 
opening  laterally,  their  point  of  junction  forming  the  knee 
(genu)  of  the  internal  capsule.  Through  this  narrow  space 
pass  the  fibres  which  connect  the  cortex  of  the  hemisphere  with 
the  lower-lying  parts  of  the  brain.  The  anterior  hmb  consists 
of  fibres  which  connect  the  thalamus  with  the  cortex;  the 
anterior  two-thirds  of  the  posterior  limb  contain  fibres  which 
conduct  impulses  to  the  motor  nuclei  of  the  pons  and  of  the 
peripheral  nerves, — i.e.,  motor  fibres, — while  through  the 
posterior  one-third  of  this  limb  pass  fibres  which  convey  im- 
pulses from  the  peripheral  nerves  to  the  cortex:  i.e.,  sensory 
fibres. 

The  amygdaloid  nucleus,  previously  mentioned,  is  a  thick- 
ened portion  of  the  cortex  of  the  temporal  lobe:  it  receives 
the  stria  terminaHs,  and  is  continuous  with  the  claustrum  and 
with  the  tail  of  the  caudate  nucleus. 

The  Fornix  and  the  Hippocampus.- — -The  fornix  is 
formed  by  two  cords  which  are  triangular  on  cross-section, 
with  the  bases  facing  each  other,  the  thin  edges  looking 
lateralward.  These  cords  diverge  behind,  converge  in  front; 
the  diverging  portions  are  connected  with  each  other  and  with 
the  ventral  surface  of  the  corpus  callosum  by  transverse  fibres 
known  as  the  lyra  (commissura  hippocampi).  Owing  to  these 
fibres,  the  fornix  appears  triangular,  with  its  apex  forward  and 
its  base  backward.  At  the  apex  of  the  fornix,  about  midway 
between  the  two  extremities  of  the  corpus  callosum,  the  cords 
separate,  and,  under  the  name  of  columns  of  the  fornix  (col- 


THE    IXTEEXAL    AXATOMT    OF    THE    EXCEPHALOX. 


rase- Dent 


In f- con 
-Hipp 

2)entfis5. 


Hipp 


-com: 


Fig.  ST.— Inf.  cor.,  Inferior  liorn  of  lateral  ventricle.  Hipp.,  Hippocam- 
pus. Fasc.  Dent,  Dentate  fascia.  Dent,  fiss.,  Dentate  fissure.  Hipp,  conv., 
Hippocampal  convolution.     Fimb.,  Fimbria.      (After  Edinger.) 


78  THE    AXATOMY    OF    THE    BEAIX. 

umnas  fomicis),  run  toward  the  liypotlialaums  to  terminate  in 
the  corpora  niamillaria.  Anterior  to  them  as  they  diverge  can 
be  seen  the  transverse  band  called  the  anterior  commissure 
(commissura  anterior  cerebri).  Between  the  column  of  the 
fornix  and  the  anterior  tubercle  of  the  thalamus  on  each  side 
is  the  opening  of  a  Y-shaped  canal  connecting  the  third  with 
the  lateral  ventricles;  it  is  called  the  foramen  of  Monro. 
From  the  point  where  the  fornix  ceases  to  be  adherent  to  the 
ventral  surface  of  the  corpus  callosum  by  means  of  the  lyra 
appears  a  new  structure, — the  septum  pellucidum, — forming 
the  dividing  wall  between  the  lateral  ventricles.  On  section 
it  is  found  to  consist  of  two  laminae  separated  by  a  very  nar- 
row cavity:    the  ca\Tim  septi  pellucidi. 

Posteriorly,  each  cord  of  the  fornix,  under  the  name  of 
crus,  enters  the  inferior  horn  of  the  ventricle,  where  it  be- 
comes continuous  Avith  the  hippocampus,  and  takes  the  name 
of  fimbria ;  it  is  accompanied  by  the  chorioid  plexus  from  the 
central  portion  of  the  ventricle. 

To  examine  the  hippocampus  a  horizontal  section  should 
be  made  through  the  region  of  the  inferior  horn  (Fig.  37). 
It  will  be  seen  that  the  hippocampus  is  a  ridge  thrown  up  by 
the  dentate  fissure  on  the  medial  surface  of  the  hemisphere, 
and  that  it  is  continuous  with  the  hippocampal  convolution 
(Fig.  38).  In  other  words,  it  is  an  infolded  portion  of  the 
cortex.  Both  gray  and  white  matter  are  folded,  but  the  white 
ceases  s'ooner  than  the  gray,  which,  continuing,  bends  first 
lateralward  and  then  toward  the  median  line,  to  terminate  in 
a  free  edge,  which,  because  of  its  serrated  appearance,  is 
known  as  the  dentate  fascia  (fascia  dentata).  It  is  not  in  the 
cavity  of  the  lateral  ventricle,  but  is  continuous  over  the 
posterior  extremity  of  the  corpus  callosum  Avith  the  fasciola 
cinerea  and  the  longitudinal  stria,  and  through  them  with  the 
gyrus  subcallosus.  All  these  structures — fascia  dentata,  fas- 
ciola cinerea,  longitudinal  strife,  and  gyrus  subcallosus— may 
be  considered  as  a  rudimentary,  or  "aborted,"  convolution,  and 
together  represent  the  free  edge  of  the  cortex  of  the  hem- 
isphere. 

Many  of  the  axones  of  the  cells  of  the  hippocampus  enter 
the  fimbria  of  the  fornix,  whence  some  of  them -cross  the 


THE    INTEKXAL    AXATOMY    OF    THE    EXCEPHALOX. 


79 


CorpcaL 


i^^<^E_.     GMChl. 


Spl 


Ant.  com.     , 
Col.For: 


conv. 


Fig.  38. — G.,  Genu  of  corpus  callosum.  Eep.  pel.,  Septum  pellucidum. 
Corp.  cal.,  Corpus  callosum.  Snl.  C.  C,  Sulcus  of  corpus  callosum.  Gy.  cin., 
Gyrus  cinguli.  Spl.,  Splenium  of  corpus  callosum.  P.  for.,  Crus  of  fornix. 
Fas.  den.,  Fascia  dentata.  Fiml).,  Fimbria.  Hip.  conv.,  Hippocampal  con- 
volution. Unc,  Uncus.  Col.  for.,  Column  of  fornix  Ant.  com..  Anterior 
commissure.    L.  t.,  Lamina  terminalis.     (After  Van  Gehuchten.) 


80  THE   ANATOMY    OF   THE    BEAHsT. 

median  line  in  the  lyra  to  enter  the  fimbria  of  the  opposite 
side  and  end  in  the  liippocampus.  Others  continue  forward 
in  the  fornix  to  the  column,  by  which  most  of  them  are  con- 
ducted to  the  corpus  mamillare;  but  some  enter  the  septum 
pellucidum  and  pass  to  the  uncus  of  the  hippocampal  con- 
volution, while  still  others  probably  turn  backward  in  front  of 
the  foramen  of  Monro,  and  run  through  the  stria  meduUaris 
of  the  thalamus  to  the  trigonum  habenulae. 

The  Chorioid  Plexus,  Velum  Interpositum,  and  Trans- 
verse Fissure. — To  the  unaided  eye  both  the  chorioid  plexus 
and  the  lateral  half  of  the  dorsal  surface  of  the  thalamus  ap- 
pear to  lie  in  the  floor  of  the  lateral  ventricle.  As  a  matter 
of  fact,  both  are  outside  of  that  cavity,  being  covered  dorsally 
by  a  layer  of  epithelium  passing  between  the  free  edge  of  the 
fornix  and  the  stria  terminalis.  Just  as  we  saw  in  the  study 
of  the  fourth  ventricle  that  the  dorsal  wall  of  the  rhomben- 
cephalon ceases  to  form  nervous  tissue  along  a  line  corre- 
sponding to  the  free  edge  of  the  posterior  medullary  velum, 
so  here,  along  a  line  corresponding  to  the  free  edge  of  the 
fornix  all  the  way  from  the  foramen  of  Monro  to  the  termina- 
tion of  the  fimbria  in  the  inferior  horn,  the  dorsal  wall  of  the 
telencephalon  ceases  to  lay  down  nervous  tissue,  and  stretches 
in  its  primitive  epithelial  state  over  the  chorioid  plexus  and 
the  thalamus  to  the  stria  terminalis,  Avhere,  again,  nervous 
tissue — i.e.,  the  diencephalon — is  developed.  As  it  passes 
over  the  plexus  and  the  lateral  half  of  the  dorsal  surface  of 
the  thalamus  it  becomes  firmly  attached  to  these  structures. 
At  the  edge  of  the  fornix  and  at  the  stria  terminalis  it  is  con- 
tinuous with  the  general  ependymal  epithelium  of  the  ven- 
tricle. 

If  the  fornix  be  cut  across  near  its  apex  and  turned  back- 
ward (Fig.  39),  there  is  exposed  the  triangular  flap  of  pia 
mater  called  the  velum  interpositum  (tela  chorioidea  ven- 
triculi  tertii).  Its  apex  is  forward  just  behind  the  apex  of  the 
fornix,  while  its  sides,  which  are  elevated  into  the  vascular 
tufts  which  we  have  called  the  chorioid  plexuses,  project  be- 
yond the  edge  of  the  fornix,  and  invaginate  the  epithelium 
both  in  the  central  portion  and  in  the  inferior  horns  of  the 
ventricle.     It  is  composed  of  two  layers.     Bearing  in  mind 


THE    IKTEKXAL    AXAT0:MY    OF    THE    EXCEPHALOX. 


81 


Anbcor: 

_-  Jfucl  Caud 


^--^Post.cor. 


Fig.  39. — St.  term.,  Stria  terminalis.  Thai.,  Thalamus.  Hipp.,  Hippo- 
campus. Fimh.,  Fimbria.  Aiit.  cor.,  Anterior  cornu  of  lateral  ventricle.  Kticl. 
cavd..  Nucleus  caudatus.  Col.  for.,  Columns  of  the  fornix.  Tel.  int..  Velum 
interpositum.  Ch.  pi.,  Chorioid  plexus.  C'al.  av.,  Calcar  avis.  Post,  eor., 
Posterior  cornii  of  lateral  ventricfe.     (After  Gray.) 


82  THE    ANATOMY    OF    THE    BEAIN. 

that  tlie  liemisplieres  in  tlie  embryo  undergo  great  growth  in 
the  posterior  direction  and  that  the  pia  mater  closely  invests 
the  surfaces  of  the  encephalon,  it  will  be  understood  that  in 
the  course  of  development  two  layers  of  the  pia,  one  covering 
the  dorsal  wall  of  the  telencephalon  and  the  other  that  of  the 
diencephalon,  Avould  be  early  brought  together,  and  caught, 
as  it  were,  between  these  two  growing  vesicles.  The  space 
through  which  the  velum  enters  the  cerebrum  is  the  trans- 
verse fissure  of  Bichat  (fissura  transversa  cerebri).  It  may  be 
compared  to  a  horseshoe  in  shape,  the  dentate  fissures  furnish- 
ing the  lateral  arms  of  the  shoe,  while  the  cross-bar  is  the 
space  between  the  posterior  extremity  of  the  corpus  callosum 
dorsally  and  the  pineal  body  and  the  mesencephalon  ventrally. 
It  is  not  a  fissure  in  the  sense  of  a  cleft  opening  into  the 
lateral  ventricles,  for,  as  we  follow  the  space  toward  these 
cavities,  we  find  that  its  bottom  is  closed  by  the  epithelium 
before  described  as  extending  between  the  edge  of  the  fornix 
and  the  stria  terminalis,  and  investing  the  chorioid  plexuses 
and  the  lateral  half  of  the  dorsal  surface  of  the  thalamus. 

The  ventral  surface  of  the  velum  is  adherent  to  the  epi- 
thelial roof  of  the  third  ventricle,  which  constitutes  its  lamina 
epithelialis.  Between  this  epithelium  and  the  pia  there  runs, 
in  an  antero-posterior  direction,  on  each  side  of  the  median 
line  the  chorioid  plexus  of  the  third  ventricle. 

The  Anterior  Co^imissure. — This  band  of  fibres  has 
been  referred  to  as  running  transversely  in  front  of  the  col- 
umns of  the  fornix.  As  it  is- chiefly  concerned  with  the  con- 
nections of  the  rhinencephalon,  it  will  be  considered  later. 

The  White  Matter  oe  the  Pallium. — The  pallium  is 
the  name  given  to  the  gray  cortex  and  the  central  white 
matter.  The  latter  may  be  divided  into  three  classes  of  fibres 
as  follow^s: — 

(A)  Fibres  of  association,  or  those  which  connect  two 
parts  of  the  same  hemisphere.  Of  these  there  are  two'  sets : 
the  long  and  the  short.  The  latter  are  all  those  innumerable 
fibres  which  connect  neighboring  points  of  the  cortex  (fibrse 
proprise).  The  long  connect  two  or  more  lobes,  and  are  ar- 
ranged in  four  fairly  distinct  bundles  (Fig.  40) : — 

1.   The   superior  longitudinal  bundle   (fasciculus  longi- 


THE    IXTEKXAL    ANATOMY    OF    THE    EXCEPHALOX.  83 


Fib.  .prop- 


lonj'^if- 


Fig.  40.— Scheme  of  fibres  of  association  of  cerebral  hemisphere  (after 
Van  Gehuchten).  Fih.  prop.,  Fibres  proprise.  F.  Long,  sup.,  Fasciculus  longi- 
tudinalis  superior.  F.  Long,  inf.,  Fasciculus  longitudinalis  inferior.  Cing., 
Cingulum.     F.  itncif.,  Fasciculus  uncinatus. 


84  THE    AXATOMY    OF    THE    BEAIX. 

tudinalis  superior),  which  conuects  the  frontal  with  the  occip- 
ital and  temporal  lobes. 

2.  The  inferior  longitudinal  bundle  (fasciculus  longi- 
tudinalis  inferior),  connecting  the  occipital  and  temporal 
lobes. 

3.  The  cingulum,  which  arches  in  the  gyrus  cinguli  from 
the  frontal  to  the  temporal  lobe. 

4.  The  uncinate  bundle  (fasciculus  uncinatus),  uniting 
the  ventral  frontal  convolution  with  the  uncus  of  the  tem- 
poral lobe. 

(B)  Commissural  fibres,  or  those  which  connect  convo- 
lutions in  one  hemisphere  with  corresponding  convolutions  in 
the  other,  such  as  the  corpus  callosum  and  the  lyra  (com- 
missura  hippocampi). 

(C)  Projection-fibres,  or  those  Avhich  connect  the  cortex 
with  lower-lying  portions  of  the  central  nervous  system. 
These,  as  we  have  seen,  pass  through  the  internal  capsule; 
their  radiation  from  the  cortex  to  the  capsule  is  called  the 
corona  radiata.  They  are  of  such  importance  that  a  separate 
chapter  will  be  devoted  to  them. 

The  Ehinekcephalox. — There  are  many  deficiencies  in 
our  knowledge  of  the  rhinencephalon,  but  the  following  state- 
ments seem  warranted  at  present.  The  principal  constituents 
of  the  olfactory  bulb  are  the  numerous  large  cells  around 
whose  dendrites  the  fibres  of  the  olfactory  nerves  terminate. 
These  cells  send  their  axones  backward  to  form  the  olfactory 
tract;  on  arriving  at  the  trigonum,  they  separate  into  two 
roots,  or  striae.  The  medial  root  ends  in  the  trigonum  and 
the  gyrus  subcallosus.  The  lateral  root  enters  the  uncus  of 
the  hippocampal  convolution,  where  most  of  its  axones  ter- 
minate; but  some  after  crossing  in  the  anterior  commissure 
turn  forward  into  the  lateral  stria  and  tract  of  the  opposite 
side,  to  end  in  the  bulb.  The  anterior  extremity  of  the  hippo- 
campal convolution  is  connected  with  the  hippocampal  eon- 
volution  of  the  opposite  side  by  the  anterior  commissure,  and 
with  the  hippocampus  of  the  same  side  by  fibres  running  in 
the  fornix,  as  already  described.  The  hippocampus,  in  its 
turn,  is  connected  by  the  column  of  the  fornix  with  the  cor- 
pus mamillare,   by  the   stria  medullaris   with   the   trigonum 


THE    IXTEKXAL    AXATOMY    OF    THE    EXCEPHALOX.  85 

liabenulas,  and  by  the  lyra  with  the  hippocampus  of  the  op- 
posite side.  In  man  the  olfactory  apparatus  must  be  regarded 
as,  to  a  large  extent,  rudimentary,  but  from  analogy  with  cer- 
tain of  the  lower  animals  in  whom  the  apparatus  receives  full 
development,  there  seems  no  doubt  that  the  entire  gyrus 
fornicatus,  the  hippocampus,  the  fornix,  the  anterior  com- 
missure, the  fascia  dentata,  and  the  fasciola  cinerea  are  all 
concerned  with  the  sense  of  smell. 


CHAPTER  IV. 

The  Coxducting-patiis  of  the  E^•CEPHALOx. 

The  cortex  of  each  hemisphere  of  the  telencephahjn  is 
in  communication  with  the  opposite  half  of  the  body  by  means 
of  fibres  conducting  impulses  to  and  from  it.  These  fibres 
may  be  divided  into  two  sets,  according  to  the  direction  of 
conduction:  centrifugal,  or  motor,  which  conduct  excitations 
from  the  cortex  to  the  various  muscles  of  the  body;  and  cen- 
tripetal, or  sensory,  which  convey  excitations  from  the  skin, 
mucous  membranes,  bones,  special  sense-organs,  etc.,  to  the 
cortex,  Avliere  are  produced  in  an  unknown  way  what  we  call 
sensations.  Each  half  of  the  body  is  thus  represented  in  or 
projected  upon  the  cortex  of  the  opposite  hemisphere;  hence 
the  name  of  '^projection-fibres"  given  to  those  fibres  of  the 
telencephalon  through  which  the  communication  is  main- 
tained. They  are  in  many  instances  collected  into  distinct 
bundles;  so  that  we  may  speak  of  motor  and  sensory  paths 
or  tracts,  meaning  thereby  definite  groups  of  fibres  along 
which  motor  or  sensory  impulses,  as  the  case  may  be,  habit- 
ually travel.  Moreover,  these  groups  of  fibres  often  arise  from 
or  terminate  in  fairly-definite  areas  of  the  cortex,  which  areas 
are  usually  called  centres.  Thus,  that  area  from  which  spring 
the  fibres  that  conduct  impulses  to  the  muscles  which  produce 
the  movements  of  the  hand  may  be  called  the  motor  '^centre" 
of  the  hand ;  that  which  receives  the  fibres  along  which  visual 
impressions  travel  is  the  "centre"  of  sight. 

The  Principal  Motor  Path. — This  path  is  formed  by 
two  groups  of  neurones.  The  cell-bodies  of  the  first  group 
are  contained  in  the  cortex,  and  their  axones  terminate  in  the 
nuclei  of  the  motor  peripheral  nerves  on  the  opposite  side  of 
the  nervous  axis, — in  the  mesencephalon,  pons,  medulla,  and- 
spinal  cord,— where  they  enter  into  conduction-relation  with 
the  second  group  of  neurones,  whose  medullated  axones  con- 
stitute the  motor  peripheral  nerves.  We  are  directly  con- 
cerned in  this  place  onlv  with  the  first,  or  cortical,  neurones. 

(86) 


THE    COXDUCTIN'G-PATHS    OF    THE    EXCEPHALOX.  87 

Their  cell-bodies  are  found  in  the  cortex  of  the  convolutions 
around  the  central  sulcus  of  Rolando:  the  anterior  central 
convolution  and  the  posterior  extremities  of  the  other  frontal 
convolutions,  the  posterior  central  convolution,  and  the  para- 
central lobule,  which  collectively  are  called  the  "motor  area" 
of  the  cortex.  In  a  general  way,  we  may  say  that  the  ventral 
portion  of  this  area  is  the  motor  centre  for  the  head,  the  mid- 
dle portion  that  for  the  upper  extremity,  and  the  dorsal  por- 
tion that  for  the  lower  extremity.  The  axones  of  the  cells  in 
this  area  converge  toward  the  internal  capsule,  and  pass 
through  the  anterior  two-thirds  of  its  posterior  limb.  In  the 
capsule  the  fibres  destined  to  reach  the  nuclei  of  the  facial  and 
hypoglossal  nerves  occupy  the  genu,  and  hence  are  called  the 
geniculate  fasciculus.  Posterior  to  them  are  the  fibres  for 
the  upper  extremity,  and  behind  these  are  those  for  the  lower 
extremity  (Fig.  31).  From  the  capsule  the  fibres  of  this  path 
enter  the  base  of  the  peduncle  of  the  cerebrum;  here  the 
geniculate  fasciculus  occupies  the  medial  border  of  the  pe- 
duncle, while  the  other  fibres  of  the  path  lie  in  the  middle  of 
that  structure.  In  the  mesencephalon,  it  will  be  recalled,  are 
the  nuclei  of  the  third  and  fourth  cranial  nerves;  they  prob- 
ably receive  fibres  from  this  path,  but  neither  the  cortical 
origin  nor  the  course  of  such  fibres  is  known. 

From  the  peduncle  the  path  reaches  the  pons,  where  some 
of  its  fibres  cross  the  median  line  to  terminate  in  the  nuclei 
of  the  motor  nerves  there  found.  jSText,  the  path  appears  in 
the  medulla  as  the  pyramid,  for  which  reason  it  is  frequently 
called  the  pyramidal  tract  throughout  its  extent.  In  this  re- 
gion fibres  are  distributed  to  the  motor  nuclei  of  the  ninth, 
tenth,  eleventh,  and  twelfth  cranial  nerves,  chiefly  of  the 
opposite  side.  At  the  spinal  extremity  of  the  medulla  the 
majority  of  the  fibres  cross  to  the  lateral  column  of  the  op- 
posite side  of  the  spinal  cord,  in  which  they  constitute  the 
crossed  pyramidal  tract  (fasciculus  cerebro-spinalis  lateralis), 
which  traverses  the  whole  length  of  the  cord,  abandoning 
fibres  to  the  ventral  horn  as  it  goes,  thus  making  connection 
with  the  spinal  lower  motor  neurones.  The  small  part  of  the 
tract  which  does  not  cross  in  the  medulla  at  the  decussation 
forms  the  direct  pyramidal  tract  (fasciculus  cerebro-spinalis 


88  THE   ANATOMY    OP   THE    BEAIN. 

anterior)  in  tlie  ventral  column  of  the  cord,  whence  its  fibres, 
in  large  part,  cross  successively  in  the  ventral  white  com- 
missure, to  end  in  the  ventral  horn  of  the  opposite  side. 

The  Secondary  Motor  Path. — There  exists  an  anatom- 
ical basis  for  a  second  motor  path  from  the  cortex  of  the  tel- 
encephalon to  the  motor  nuclei  of  the  peripheral  nerves, 
though  it  cannot  be  traced  with  the  same  distinctness  as  the 
preceding,  nor  is  much  known  concerning  its  function.  It  is 
formed  by  at  least  four  groups  of  neurones,  three  of  which  are 
in  the  encephalon.  The  cells  of  the  cortical  neurones  lie  in  the 
same  area  as  those  of  the  principal  path,  and  also  in  the  cor- 
tex of  the  temporal  lobe.  They  send  their  axones  through  the 
anterior  two-thirds  of  the  posterior  limb  of  the  internal  cap- 
sule, whence  they  enter  the  base  of  the  peduncle  of  the  cere- 
brum. Here  those  which  arise  in  the  "motor  area"  occupy 
the  same  position  with  the  principal  motor  path,  while  those 
which  arise  in  the  temporal  lobe  lie  in  the  lateral  part  of  the 
peduncle  (Fig.  41).  All  these  fibres  terminate  in  the  nuclei 
pontis;  whence  the  name  of  cortico-pontile  given  to  them. 
The  cells  of  the  nuclei  pontis^  which  are  the  second  group  of 
neurones,  send  their  axones  across  the  median  line  to  enter  the 
cerebellar  hemisphere  and  terminate  around  Purkinje's  cells 
in  the  cortex.  These  Purkinje  cells  constitute  the  third  group 
of  iTeurones,  but  the  course  pursued  by  their  axones  is  unde- 
cided; there  is  good  reason  for  believing  that  they  reach  the 
ventral  horn  of  the  spinal  cord,  either  directly  or  indirectly 
through  the  olive. 

The  Principal  Sensory  Path. — The  portions  of  each 
half  of  the  spinal  cord  believed  to  conduct  the  various  Centrip- 
etal impressions  from  the  skin,  muscles,  and  viscera  are  the 
funiculi  of  GoU  and  Burdach,  and  the  ventro-lateral  ground- 
bundle.  The  latter  of  these  is  formed  by  fibres  which  spring 
from  cells  in  the  gray  matter  of  the  opposite  side  of  the  cord, 
while  the  two  funiculi  first  mentioned  contain  the  central 
axones  of  the  ganglia  on  the  dorsal  roots  of  the  spinal  nerves 
of  the  same  side.  It  will  be  recalled  that  the  ventro-lateral 
ground-bundle  on  reaching  the  medulla  lies  dorsal  to  the 
pyramid,  and  that  the  two  dorsal  funiculi  of  the  cord  ter- 
minate in  their  respective  nuclei,  the  cells  of  which  send  axones 


THE    CONDUCTING-PATHS    OF    THE    ENCEPHALOX. 


89 


Fig.  41. — /,  Eegion  of  temporo-pontile  fibres.  //,  Region  of  pyramidal 
tracts.  ///,  Eegion  of  geniculate  fasciculus.  S.  n.,  Substantia  nigra.  (After 
Dejerine.) 


90  THE    AXATOilY    OF    THE    BEAIX. 

across  the  median  line  as  internal  arcnate  fibres,  to  enter  first 
the  interolivary  layer  and  later  the  medial  lemniscus.  This 
medial  lemniscus  is  the  principal  sensory  path  in  the  enceph- 
alon.  We  have  traced  it  through  the  medulla,  where  it  lies 
medial  to  the  olive  and  lateral  to  the  raphe;  thence  into  the 
pons,  where  it  becomes  flattened  and  lies  dorsal  to  the  deep 
transverse  fibres;  and  thence  into  the  tegmentum  of  the  mes- 
encephalon, where  it  fuses  laterally  with  the  lateral  lemniscus. 
In  its  course  through  the  rhombencephalon  it  is  joined  by 
fibres  derived  from  the  terminal  nuclei  of  the  sensory  nerves 
there  found;  these,  as  we  have  seen,  constitute  many  of  the 
internal  arcuate  fibres,  and  join  the  lemniscus  of  the  opposite 
side  from  that  in  which  they  arise.  The  axones  from  the  nuclei 
of  the  cochlear  nerve,  however,  have  a  separate  path.  From 
the  mesencephalon  the  medial  lemniscus  enters  the  dienceph- 
alon,  where  the  majority,  at  least,  of  its  fibres  end  in  the  ventral 
nucleus  of  the  thalamus.  Here  are  the  cells  of  the  last  group 
of  neurones,  whose  axones  pass  through  the  posterior  third 
of  the  posterior  limb  of  the  internal  capsule  to  terminate  in 
the  cortex  of  the  telencephalon  over  an  area — the  somsesthetic 
area — which  practically  coincides  with  that  which  we  have 
termed  the  motor  area.  It  will  be  noticed  that  this  path,  like 
the  principal  motor  path,  is  crossed.  It  is  formed  by  three 
superimposed  groups  of  neurones  as  follows:  (1)  the  periph- 
eral, whose  peripheral  axones  form  the  peripheral  sensory 
nerves  and  whose  central  axones  build  up  the  dorsal  funiculi 
of  the  cord;  (2)  the  spinal  and  rhombencephalic,  whose  axones 
form,  respectively,  the  ventrb-lateral  ground-bundle  of  the 
cord  and  the  internal  arcuate  fibres  and  medial  lemniscus ;  and 
(3)  the  thalamo-cortical,  whose  axones  complete  the  connection 
with  the  cortex. 

The  Secok^daey  Sensory  Path. — As  in  the  case  of  motor 
impulses,  so,  for  the  sensory,  there  exists  the  anatomical  basis 
of  a  complex  secondary  path.  The  two  cerebellar  tracts  from 
the  cord — the  direct  cerebellar  tract  and  the  main  mass  of 
Gowers's  tract — terminate  in  the  cerebellum ;  moreover,  some 
of  the  sensory  cranial  nerves,  notably  the  trigeminal  and  the 
vestibular  portion  of  the  acoustic,  send  some  fibres  into  the 
cerebellum,  as  do  also  the  terminal  nuclei  of  the  dorsal  fu- 


THE    COXDUCTIXG-PATHS    OF    THE    ENCEPHALON.  91 

niciili  of  the  cord.  Thus  there  are  numerous  fibres  conduct- 
ing centripetallj  as  regards  tlie  cerebellum.  From  the  latter 
fibres  run  in  the  anterior  peduncle  to  the.  red  nucleus  of  the 
mesencephalon  on  the  opposite  side;  the  red  nucleus  sends 
fibres  into  the  thalamus  of  the  same  side,  and  from  the  thal- 
amus, as  we  have  seen,  many  fibres  proceed  to  the  cortex.  So 
that  it  seems  quite  possible  that  certain  sensory  impressions 
may  reach  the  cortex  by  this  roundabout  path. 

The  Acoustic  Path. — The  path  traveled  by  auditory 
impressions  is  composed  of  four  groups  of  neurones.  The  cen- 
tral axones  of  the  peripheral  neurones  form  the  cochlear  portion 
of  the  acoustic  nerve,  which  terminates  in  the  two  gray  masses 
known  as  the  dorsal  and  ventral  nuclei  of  the  cochlear  nerve. 
These  two  nuclei  contain  the  cells  of  the  second  group  of  neu- 
rones. Those  of  the  ventral  nucleus  send  their  axones  into  the 
pons,  to  form  the  trapezoid  body.  The  fibres  of  this  body 
undergo  a  partial  decussation,  some  of  them  terminating  in 
the  anterior  olive  of  the  same  side,  while  others  cross  the 
raphe  to  reach  the  anterior  olive  of  the  opposite  side.  This 
olive  furnishes  the  third  group  of  neurones;  their  axones  run 
forward,  and,  aided,  perhaps,  by  the  acoustic  striae  from  the 
dorsal  nucleus  of  the  opposite  side,  form  the  lateral  lemniscus, 
which  ends  in  the  medial  geniculate  body  and  in  the  posterior 
colliculus.  In  these  two  bodies  the  fourth  group  of  neurones 
is  found;  their  axones  enter  the  posterior  third  of  the  poste- 
rior limb  of  the  internal  capsule,  and  terminate  in  the  dorsal 
(superior)  convolution  of  the  temporal  lobe.  It  should  be 
borne  in  mind  that  the  acoustic  path  is  only  partially  crossed, 
since  the  trapezoid  body  only  partially  decussates;  in  other 
words,  each  dorsal  temporal  convolution  is  in  communication 
with  both  ears. 

The  Optic  Path. — In  this  path  there  are  three  sets  of 
neurones.  The  cells  of  the  first  set  are  contained  in  the  retina ; 
they  are  the  bipolar  cells  of  this  membrane.  The  cell-bodies 
of  the  second  set  are  also  found  in  the  retina;  they  are  the 
so-called  ganglion-cells  of  the  retina;  their  axones  run  back- 
ward and  medialwarcl  as  the  optic  nerve  to  enter  the  chiasm. 
In  the  chiasm  the  optic  nerve  partially  decussates.  The  usual 
statement  is  that  the  nerve  undergoes  a  semidecussation,  in 


93  THE    AXATOilT    OF    THE    BEAIX. 

process  of  wliicli  the  fibres  from  the  temporal  half  of  the 
retina  emerge  from  the  chiasm  as  the  lateral  half  of  the  optic 
tract  of  the  same  side,  while  the  fibres  of  the  medial  half  of 
the  tract  are  derived  frora  the  medial  half  of  the  opposite 
retina.  However,  anatomical  investigation  has  thus  far  not 
been  able  to  establish  anything  mnch  more  definite  than  that 
a  partial  decussation  occurs  in  the  chiasm.  The  optic  tract, 
formed  thus  by  fibres  from  both  retinae,  runs  backward  and 
lateralward,  winding  first  ventral  and  then  lateral  to  the  cere- 
bral peduncle,  to  gain  the  diencephalon,  where  its  fibres  ter- 
minate in  the  lateral  geniculate  body,  the  pulvinar  of  the 
thalamus,  and  the  anterior  colliculus  of  the  mesencephalon. 
In  the  gray  matter  of  these  structures  are  the  cell-bodies  of 
the  third  group  of  optic  neurones.  Their  axones,  having  en- 
tered the  posterior  third  of  the  posterior  limb  of  the  internal 
capsule,  turn  backward,  run  through  the  occipito-thalamic 
radiation,  and  terminate  in  the  cortex  of  the  cuneus,  espe- 
cially in  the  vicinity  of  the  calcarine  fissure. 

It  seems  established  that  the  optic  tract  and  nerve  also 
contain  fibres  which  conduct  centrif ugally :  i.e.,  fibres  which 
run  from  the  lateral  geniculate  body,  anterior  colliculus,  and 
thalamus  to  the  retina?. 

The  Olfactory  Path. — This  path  is  constituted  of  two 
sets^f  neurones.  The  axones  of  the  peripheral  set,  the  olfac- 
tory nerves,  terminate  in  the  bulb,  where  the  cells  of  the 
second,  or  central,  set  are  situated.  The  axones  of  these  are 
directed  backward  as  the  olfactory  tract,  which  divides  into 
the  two  olfactory  roots,  or  strise.  The  medial  stria  ends  in 
the  olfactory  trigonum,  the  gyrus  subcallosus,  and  the  ad- 
jacent portion  of  the  gyrus  fornicatus;  the  lateral  stria  ter- 
minates in  the  hippocampal  convolution,  especially  in  the 
neighborhood  of  its  uncus.  Hence  these  areas  of  the  cortex 
may  be  considered  olfactory  centres.  From  them  proceed 
paths  which  throw  the  lower  motor  neurones  under  the  in- 
fluence of  the  sense  of  smell,  thus  accounting  for  olfactory 
reflexes. 


IXDEX. 


Ala  cinerea,  10,  4G. 

Aqueduct  of  Sylvius,  4,  19,  60. 

Area,  parolfactoi'ia.  33. 

the  acoustic,  10,  12,  46. 
Axis,  the  neural,  1. 

Basis  pedunculi,  62. 

Body,  the  pituitary,  22. 

Brachium  quadrigeminum  inferius,  18. 

"superius,  18. 
Bulb,  the  olfactory,  33. 

Calamus  scriptorius,  8. 

Calear  avis^  72. 

Canal,  the  central,  of  medulla,  40. 

the  neural,  1. 
Capsule,  the  external,  76. 

the  internal,  66,  74,  76. 
Centrum  semiovale,  70. 
Cerebellum,  2. 

connections  of,  58,  59. 

internal  anatomy  of,  58. 

surface  anatomy  of,  12. 
Cerebrum.  4,  24. 
Chiasm,  the  optic,  20,  22. 
Cingulum,  24. 
Claustrum,  76. 
Clava,  8. 
Colliculus,  facialis,  12. 

inferior,  18. 

internal  anatomy  of,  64. 

superior,  18. 
Columns  of  fornix,  78. 
Commissure,  anterior,  of  cerebrum,  78. 
82. 

of  the  habenulae,  21. 

of  the  hippocampus,  76. 

posterior,  of  the  cerebrum,  21. 
Convolution  or  convolutions,  angular. 
28. 

ascending  frontal  (precentral) ,  26. 

ascending    parietal     (postcentral), 
26. 

calloso-marginal,  32. 

fusiform,  28. 

hippocampal.  30,  32. 

inferior  frontal,  26. 

inferior  temporal,  28. 

middle  frontal.  26. 

middle  temporal,  28. 


Convolution  or  convolutions,  occipital, 
30. 

of  corpus  callosum,  30. 

orbital,  26. 

straight,  26. 

superior  frontal,  26. 

superior  temporal,  28. 

supramarginal,  28. 
Corpora  quadrigemina,  2,  18,  62. 
Corpus  callosum,  24,  70,  72. 

geniculatum  laterale,  20,  70. 
mediale,  20,  70. 

mamillare,  22,  68. 

pineale,  21. 

restiforme,  8,  18,  46. 

striatum,  24J   66,  74. 

trapezoideum,  48,  52. 
Crura  of  fornix,  78. 
Cuneus,  30. 

Decussation    of   anterior    peduncles    of 
cerebellum,  60. 

of  lemnisci,  38. 

of  optic  nerves,  91. 

of  pyramids,  6,  36. 
Diencephalon,  2. 

intei'nal  anatomy  of,  66. 

surface  anatomy  of,  19. 

Eminentia  medialis,  12. 
Encephalon,  the  divisions  of,  1,  2. 
Ependymal  epithelium,  2. 
Epithalamus,  4. 

surface  anatomy  of,  21. 

Fascia  dentata,  78. 

Fasciculi   longitudinales    of   pons   Va- 
rolii, 50. 
Fasciculus,  inferior  longitudinal.  84. 

medial  longitudinal,  42,  46,  56,  64. 

retroflexus.  62. 

superior  longitudinal,  82. 

thalamo-mamillaris,  68. 

uncinatus,  84. 
Fasciola  cinerea,  70.  78. 
Fibres,    association    of    telencephalon. 
84. 

cerebello-olivary,  40,  46. 

commissural  of  telencephalon.  84. 

cortico-pontile,  56. 

external  arcuate.  46. 

(93) 


94 


IXDEX. 


Fibre?,  internal  arcuate,  38,  40,  44. 

projection  of  telencephalon.  84. 

transverse  of  pons  Varolii,  50. 
Fissure,  ealcarine.  30. 

collateral.  30. 

dentate,  30.  72. 

dorsal  median,  8. 

horizontal,  14. 

longitudinal,  of  cerebrum.  24. 

of  Sylvius.  24. 

paramedian,  8. 

parieto-occipital.  25,  30. 

transverse  of  Bichat.  82. 

transverse  of  cerebellum.  14. 

ventral  median,  6. 
Flocculus,  14. 
Foramen,  of  ]Magendie,  16. 

of  ]Monro,  76. 
Formatio  reticularis,  36. 
Fornix,  76. 
Fossa  interpeduneularis,  18. 

rhomboidea.  8,  15. 
Fovea  inferior.  18. 

superior.  18. 
Frenulum,  18. 
Funiculus  of  Burdach.  8. 

of  GoU,  18. 

Ganglion  interpedunculare,  62. 
Globus  pallidus.  74. 
Gyri  transitivi,  26. 
Gyrus,  fornieatus.  32.  ^ 

subcallosus.  33.  72. 

HabenuJa.  21. 

Hemispheres  of  telencephalon.  24. 

lateral  surface  of.  24. 

medial  surface  of.  30. 
Hippocampus.' 72,  78. 
Hypophysis,  22. 
Hypothalamus,  4.  14. 

internal  anatomy  of,  68. 

surface  anatomy  of.  22. 

Incisure,  dorsal,  of  cerebellum.  14. 

ventral,  of  cerebellum,  14. 
Infundibulum.  22.  68. 
Island  of  Eeil.  25,  30,  76. 

Lamina,  chorioidea  epithelialis.  16. 

terminalis.  22.  68. 
Lemniscus,  the  lateral,  10,  56,  62. 

the  medial,  38,  52,  56. 
Lingula.  14. 
Lobe,  frontal.  24,  26. 

limbic,  of  Broca.  32. 

occipital.  24.  30! 

parietal.  24.  28. 

temporal.  24.  28. 


Lobes  of  cerebelh;m.  14. 
Lobule,  inferior  parietal,  28. 

paracentral,  32. 

superior  parietal,  28. 
Locus  cceruleus.  12. 
Lyra,  76,  80. 

Mesencephalon,  2. 

internal  anatomy,  60. 

surface  anatomy,  18. 
Met^ncephalon,  2. 

internal  anatomy,  48. 

surface  anatomy,  10. 
Myelencephalon,  2. 

internal  anatomy,  34. 

surface  anatomy,  6. 

Xerve,  abducens,  8. 

acoustic,  8,  46. 

cochlear.  48. 

facial,  8'. 

glosso- pharyngeal,  6. 

hypoglossal,  6. 

oculomotor.  64. 

optic.  20.  91. 

spinal  accessory,  6,  34. 

trigeminal.  10.  54. 

trochlear,  60. 

vagus,  6. 

vestibular,  48. 
Xidus  a^^s,  14. 
Xodulus,  14. 
Nucleus  or  nuclei,  ambiguus,  42. 

amygdaloid.  74.  76. 

caudatus.  66.  74. 

central,  of  pons  Varolii,  54. 

dentatus.  58. 

dorsal  of  cochlear  nerve,  46. 

emboliformis,  58. 

fastigii,  58. 

globosus.  58. 

hypothalamicus.  68. 

lentiformis.  66,  74. 

of  abducens  nerve,  52. 

of  Bechterew,  50. 

of  Deiters,  50. 

of  facial  nen^e.  50.  52. 

of  funiculus  of  Burdach,  38. 

of  funiculus  of  Goll.  38. 

of  giosso-pharyngeal  nerve.  '42. 

of  .hypoglossa:i  nerve,  42. 

of  lateral  lemniscus.  56. 

of  oculomotor  nerve,  64. 

of  olive,  40. 

of  spinal  accessory  nerve,  34. 

of  thalamus.  66. 

of  tractus  solitarius.  42. 

of  trigeminal  nerve,  54. 


IXDEX. 


95 


Xucleus  or  neuclei,  of  trochlear  nerve, 
54,  60. 
of  vagus  nerve,  42. 
of  vestibular  nerve,  48. 
jjontis,  50. 
red,  59,  60,  62. 
superior  olivary,  52. 
ventral  of  cochlear  nerve,  48. 

Olive,  6. 
Operculum,  25,  30. 

Pallium,  24,  82. 

Path,  conducting,  85,  86. 

acoustic,  91. 

olfactory,  92. 

optic,  91. 

principal  motor,  86. 

principal  sensory,  88. 

secondary  motor,  88. 

secondary  sensory,  90. 
Peduncle,  anterior,  of  cerebellum  (bra- 
chium     conjunctivum).     10, 
18,  52. 

middle,   of   cerebellum    (brachium 
pontis) ,  10. 

of  cerebrum,  2,  18. 
Plexus,  chorioid,  of  fourth  ventricle,  16. 

of  lateral  ventricle,  78,  80. 

of  third  ventricle,  82. 
Pons  Varolii,  2. 

internal  anatomy  of,  48. 

surface  anatomy  of,  10. 
Process,  inferior  vermiform,  14. 

superior  vermiform,  14. 
Prosencephalon,  2. 
Pulvinar,  19. 
Putamen,  74. 
Pyramid,  of  medulla  oblongata,  6. 

Radiation,  occipito-thalamic.  70. 
Raphe,  38. 
Recess,  lateral,  15. 

of  infundibulum,  22. 

optic,   18. 

Rhinencephalon,  24. 

internal  anatomy  of,  85,  86. 

sui'face  anatomy  of,  32. 
Rhombencephalon,  2. 

isthmus  of,  2,  15. 
Root,  descending  of  trigeminal  ner/e, 
56. 

descending  of  vestibular  nerve,  40, 
50. 
Root-fibres,  of  abducens  nerve,  52. 

of  acoustic  nerve,  46. 

of  cochlear  nerve,  46. 

of  facial  nerve,  52. 


Root-fibres,  of  oculomotor  nerve,  64. 
of  trigeminal  nerve,  54. 
of  trochlear  ner^-e,  60. 
of  vestibular  nerA'e,  46. 

Septum  pellucidum,  78. 

Stratum  interolivare  lemnisci.  42. 

Stria  or  strise,  acoustic,  8,  46. 

lateral  longitudinal,  70. 

medial  longitudinal,  70. 

medullaris,  19. 

olfactory,  33. 

terminalis,   19. 
Sulcus,  basilaris,  10. 

calloso-marginal.  32. 

central,  of  Rolando,  25. 

chorioid.  19. 

circularis,  30. 

dorso-lateral,  6. 

inferior  frontal,  26. 

inferior  temporal,  28. 

interbrachialis,  18. 

interparietal,  28. 

lateralis,  19. 

liraitans,  10,  12. 

marginal,  32. 

median  longitudinal,  8,  12. 

middle  temporal,  28. 

of  corpus  callosum,  30. 

of  Monro,  19. 

olfactory,  26,  33. 

post-central,  26. 

precentral,  26. 

subfrontal,  32. 

subparietal.   32. 

superior  frontal,  26. 

superior  temporal,  28. 

ventrolateral.  6. 
Substantia,  corticalis,  70. 

gelatinosa,  34. 

nigra,  62. 

perforata  anterior,  24.  33. 

perforata  posterior,  18. 

Tegmentum.  62. 

Tela  chorioidea,  of  third  ventricle,  21, 
80. 

of  fourth  ventricle,  16. 
Telencephalon,  2. 

internal  anatomy  of.  70. 

surface  anatomv  of,  24. 
Tent,  14. 

Thalamencephalon.  4. 
Thalamus,  internal  anatomy  of,  66. 

surface  anatomy  of,  19. 
Tract,  crossed  pyramidal,  36. 

direct  cerebellar.  40. 


96 


INDEX. 


Tract,  direct  pyramidal,  36. 

lateral,  6. 

of  Gowers,  40,  59. 

olfactory,  33. 

optic,  19,  20,  22,  68. 

solitary,  42,  44. 

spinalj'^of  trigeminal  nerve,  34 
Trigonum,  habenulse,   19,  21. 

hypoglossal,  10,  46. 

olfactory,  33. 
Tuber  cinereum,  22,  68. 
Tubercle,  anterior,  of  thalamus,  20. 

cuneate,  8. 


Vallecula,  14. 
Valve  of  Vieussens,  12. 
Velum,  anterior  medullary,  12, 
54. 

interpositum,  80. 

posterior  medullary,  14. 
Vena  terminalis,  19. 
Ventricle,  fourth.  3,  15,  16. 

third,  4,  21. 

lateral,  4,  72. 


Worm.  14. 


14,  18, 


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